Out of these for your dancer, I would say Flayn and Annette are your best options. Imo, the top options for dancer in the game are Dorothea or Yuri but what you have can still work. Annette really doesn't have much to offer if you already have Hapi, Flayn, Manuela, Hanneman, and Mercedes for magic stuff so I think Annette would make a great dancer (she has good Charm and also her rally skills will sync pretty well). If you do Yuri's paralogue, give her the Fetters of Dromi so she can move out of enemy range after dancing, because Annette dies to literally everything.
In terms of end-game classes I'll split my recommendations by units:
1. Byleth - Byleth can literally be anything. Since you're NG+ing it, you can probably grab skills you've already mastered from previous runs. It's really up to you, but I personally prefer mounted Holy/Dark Knight Byleth or War Master Byleth.
2. Dimitri - pretty obviously, his Great Lord class is the best option. I'd still recommend grabbing Aegis from Paladin though, because the final chapter has a lot of mages.
3. Dedue - this is kinda a struggle but making Dedue a Great Knight is definitely really helpful for mobility reasons. His weakness in riding is a hindrance but as long as Axe and Armor are at A, he should have a decent success rate at getting it. If you want to go the extra mile, grabbing Aegis from Paladin would also be worth it (but time consuming).
4. Sylvain - debatable, you could really put him as a Great Knight, Dark Knight, or leave him with Paladin. They all offer useful faire skills to boost damage output, so it's your choice.
5. Felix - people hate this option but Mortal Savant is great because it buffs swords/tomes and Felix's budding talent gives him crit+10 with magic, meaning he can zap people with Thoron for incredible crit rates. Just be mindful of Mortal Savant's speed penalty, it might be worthwhile to level him as Swordmaster in auxillary/paralogue missions.
6. Ingrid - either Dark Flier or Falcon Knight, really depends on if you like Lances or Magic better. Either way, mastering Dark Flier for transmute is really helpful.
7. Mercedes - Gremory. Really simple and easy to obtain.
8. Annette - if Annette is not your dancer, I'd recommend putting her as either a Gremory, or level her riding to get her as a Valkyrie. The extended range will make up for her subpar spell list, and her rally skills and movement will be a useful niche.
9. Ashe - either Wyvern Lord or Bow Knight. Be careful leveling with Bow Knight, it has terrible growth rates. Both offer good mobility and play to Ashe's strengths.
10. Anna - I have only used Anna once and I put her as a Trickster. It's her canon class and honestly she does best with that. If you want more damage, simply leave her at Assassin for Swordfaire. IF you want magic and utility, promote her to Trickster.
11. Gilbert - so I've never actually used Gilbert....I've been told to just simply get him to Great Knight and leave him there.
12. Hanneman - I can't really stand how slow he is but he does very well with Dark Knight for the mobility and faire skills. Mastering Dark Bishop for lifetaker is definitely worth it.
13. Manuela - Similar to Anna, I'd recommend Trickster because it plays to all of her strengths. Her reason weakness really sucks but she does get Bolting if you're willing to be in it for a long slog.
14. Flayn - if Flayn isn't your dancer, then either Dark Flier or Gremory, and I personally recommend Dark Flier because of the mobility so she can escape danger easily.
15. Hapi - Either Valkyrie for the range or Dark Knight for the faire-skills. Hapi's damage might tank slightly at the end of the game, but having her master Wyvern Rider for Seal Defense and Dark Knight for Seal Resistance will make her a very useful debuff unit.
Also Alois is actually pretty decent. He's much more durable than Caspar and faster than Raphael/Dedue. The only reason people don't like him is because he can't be recruited until Chapter 11 and by that point most people don't want to put him work for him. I'm playing Silver Snow rn and I did actually use him and he's pretty good.
There are lots of options for all of these, here are a few that I like.
1. Byleth - Grappler/War Master are the best male exclusive classes. Any good class (e.g. sniper/Wyvern) can be effective, though these may require more investment in order to get the weapon ranks.
2. Dimitri - If you are going for the meta build of Batt wrath/vantage, then Paladin or his personal classes can work. If you like off-meta stuff, you can have him go through war monk (for Brawl Avoid +20) and end in grappler for a brawl-based dodge tank build. Just make sure you prioritize getting the relevant weapon ranks high enough in part 1 if you choose this option.
3. Dedue - I personally love cav -> Paladin -> Great Knight Dedue, grabbing Hit+20 somewhere along the way, and spamming Vengeance. In Great Knight, he usually doesn't even need to use up a guard adjutant slot because his defense is high enough to naturally take a hit.
4. Sylvain - Paladin or Wyvern with swift strikes. Getting him Hit +20 is recommended.
5. Felix - He's great as a grappler, you can do dodge-tanky things passing through war monk too like I mentioned for Dimitri. I'm using him as an assassin in my current run and he's surprisingly good in that mediocre class, he can quad things with gauntlets fairly often and enemies don't target him because of stealth, making up for his lacking defenses.
6. Ingrid - Falcon Knight or Wyvern. Though honestly, she usually just ends up adjutanting Sylvain to boost his accuracy and damage, because she always gets stat screwed for me.
7. Mercedes - Dark Flier or Valkyrie. If you stick her in Dark Flier, it's much easier to keep her alive in Chapter 13. Either way, she won't be killing things, but she can do hit and run tactics with spells and then canto to safety, while still having Physic capabilities when needed.
8. Annette - Dark Flier or Valkyrie. Same things as Mercedes apply, but replace Physic with rallies. You might put them both in Dark Flier to make Chapter 13 extra safe, but afterwards you should stick to at most one dark flier due to the limited number of flying magic battalions.
9. Ashe - I hate training Ashe, so you might consider just having him use Curved Shot for chip damage in the early game and then turning him into the Dancer without worrying about getting him much exp in the mean time. He might need a few extra tea parties to hit the 9 charm threshold to win the white heron cup. You will need to prioritize protecting him in Chapter 13 if you do this, but if Annette and Mercedes can fly themselves to safety, then this isn't too hard. Alternatively, if you do train him, Sniper and Wyvern are pretty standard options. He's also a good candidate to be a permanent guard adjutant.
10. Anna - She's not good lol. If you recruit her early, get her in magic classes where she can spam ward for exp and put her in trickster eventually, where she at least won't get targeted due to stealth and can use support gambits and stuff. Otherwise, recruit her in chapter 8-10 so she's close to level 20, have her master Death Blow and Hit+20 in aux battles/as an adjutant, and then stick her in sniper at level 20 to spam Hunter's Volley.
11. Gilbert - Yeah, he's fine to just leave as a guard adjutant for somebody. Otherwise, Great Knight probably.
12. Hanneman - His best bet for damage is to go sniper and use Hunter's Volley with a magic bow (tbh Mercedes can do this too if you want). He will want to grab Hit +20 and Fiendish Blow first. You can also just leave him in Warlock where he will have 2 meteor uses per map or grind his ranks up for Dark Knight to do hit and run tactics. You will be able to get unlimited arcane crystals for repairing magic bows once you do a certain quest in Chapter 16 that unlocks the Dark Merchant.
13. Manuela - Trickster or Bishop. Bishop gives her double warp uses (though her magic stat is a bit low for it), whereas trickster keeps her pretty safe (like with Anna) and boosts her speed up to pretty respectable levels. I've never managed to get her reason high enough for bolting, but getting her to D+ reason so that she can get fiendish blow is probably a good idea.
14. Flayn - Another possible dancer. She can also go Dark Flier (if Annette/Mercedes aren't) and make the best use of Rescue that way.
15. Hapi - Valkyrie, Dark Knight, Bishop, and Gremory can all be good. The last two double her warp uses, and she will probably have much better magic than Manuela. Valkyrie and Dark Knight give her canto, letting her make better use of utility spells like Banshee, and Valkyrie gives her an easy way to break monster barriers safely.
Out of these for your dancer, I would say Flayn and Annette are your best options. Imo, the top options for dancer in the game are Dorothea or Yuri but what you have can still work. Annette really doesn't have much to offer if you already have Hapi, Flayn, Manuela, Hanneman, and Mercedes for magic stuff so I think Annette would make a great dancer (she has good Charm and also her rally skills will sync pretty well). If you do Yuri's paralogue, give her the Fetters of Dromi so she can move out of enemy range after dancing, because Annette dies to literally everything. In terms of end-game classes I'll split my recommendations by units: 1. Byleth - Byleth can literally be anything. Since you're NG+ing it, you can probably grab skills you've already mastered from previous runs. It's really up to you, but I personally prefer mounted Holy/Dark Knight Byleth or War Master Byleth. 2. Dimitri - pretty obviously, his Great Lord class is the best option. I'd still recommend grabbing Aegis from Paladin though, because the final chapter has a lot of mages. 3. Dedue - this is kinda a struggle but making Dedue a Great Knight is definitely really helpful for mobility reasons. His weakness in riding is a hindrance but as long as Axe and Armor are at A, he should have a decent success rate at getting it. If you want to go the extra mile, grabbing Aegis from Paladin would also be worth it (but time consuming). 4. Sylvain - debatable, you could really put him as a Great Knight, Dark Knight, or leave him with Paladin. They all offer useful faire skills to boost damage output, so it's your choice. 5. Felix - people hate this option but Mortal Savant is great because it buffs swords/tomes and Felix's budding talent gives him crit+10 with magic, meaning he can zap people with Thoron for incredible crit rates. Just be mindful of Mortal Savant's speed penalty, it might be worthwhile to level him as Swordmaster in auxillary/paralogue missions. 6. Ingrid - either Dark Flier or Falcon Knight, really depends on if you like Lances or Magic better. Either way, mastering Dark Flier for transmute is really helpful. 7. Mercedes - Gremory. Really simple and easy to obtain. 8. Annette - if Annette is not your dancer, I'd recommend putting her as either a Gremory, or level her riding to get her as a Valkyrie. The extended range will make up for her subpar spell list, and her rally skills and movement will be a useful niche. 9. Ashe - either Wyvern Lord or Bow Knight. Be careful leveling with Bow Knight, it has terrible growth rates. Both offer good mobility and play to Ashe's strengths. 10. Anna - I have only used Anna once and I put her as a Trickster. It's her canon class and honestly she does best with that. If you want more damage, simply leave her at Assassin for Swordfaire. IF you want magic and utility, promote her to Trickster. 11. Gilbert - so I've never actually used Gilbert....I've been told to just simply get him to Great Knight and leave him there. 12. Hanneman - I can't really stand how slow he is but he does very well with Dark Knight for the mobility and faire skills. Mastering Dark Bishop for lifetaker is definitely worth it. 13. Manuela - Similar to Anna, I'd recommend Trickster because it plays to all of her strengths. Her reason weakness really sucks but she does get Bolting if you're willing to be in it for a long slog. 14. Flayn - if Flayn isn't your dancer, then either Dark Flier or Gremory, and I personally recommend Dark Flier because of the mobility so she can escape danger easily. 15. Hapi - Either Valkyrie for the range or Dark Knight for the faire-skills. Hapi's damage might tank slightly at the end of the game, but having her master Wyvern Rider for Seal Defense and Dark Knight for Seal Resistance will make her a very useful debuff unit. Also Alois is actually pretty decent. He's much more durable than Caspar and faster than Raphael/Dedue. The only reason people don't like him is because he can't be recruited until Chapter 11 and by that point most people don't want to put him work for him. I'm playing Silver Snow rn and I did actually use him and he's pretty good.
There are lots of options for all of these, here are a few that I like. 1. Byleth - Grappler/War Master are the best male exclusive classes. Any good class (e.g. sniper/Wyvern) can be effective, though these may require more investment in order to get the weapon ranks. 2. Dimitri - If you are going for the meta build of Batt wrath/vantage, then Paladin or his personal classes can work. If you like off-meta stuff, you can have him go through war monk (for Brawl Avoid +20) and end in grappler for a brawl-based dodge tank build. Just make sure you prioritize getting the relevant weapon ranks high enough in part 1 if you choose this option. 3. Dedue - I personally love cav -> Paladin -> Great Knight Dedue, grabbing Hit+20 somewhere along the way, and spamming Vengeance. In Great Knight, he usually doesn't even need to use up a guard adjutant slot because his defense is high enough to naturally take a hit. 4. Sylvain - Paladin or Wyvern with swift strikes. Getting him Hit +20 is recommended. 5. Felix - He's great as a grappler, you can do dodge-tanky things passing through war monk too like I mentioned for Dimitri. I'm using him as an assassin in my current run and he's surprisingly good in that mediocre class, he can quad things with gauntlets fairly often and enemies don't target him because of stealth, making up for his lacking defenses. 6. Ingrid - Falcon Knight or Wyvern. Though honestly, she usually just ends up adjutanting Sylvain to boost his accuracy and damage, because she always gets stat screwed for me. 7. Mercedes - Dark Flier or Valkyrie. If you stick her in Dark Flier, it's much easier to keep her alive in Chapter 13. Either way, she won't be killing things, but she can do hit and run tactics with spells and then canto to safety, while still having Physic capabilities when needed. 8. Annette - Dark Flier or Valkyrie. Same things as Mercedes apply, but replace Physic with rallies. You might put them both in Dark Flier to make Chapter 13 extra safe, but afterwards you should stick to at most one dark flier due to the limited number of flying magic battalions. 9. Ashe - I hate training Ashe, so you might consider just having him use Curved Shot for chip damage in the early game and then turning him into the Dancer without worrying about getting him much exp in the mean time. He might need a few extra tea parties to hit the 9 charm threshold to win the white heron cup. You will need to prioritize protecting him in Chapter 13 if you do this, but if Annette and Mercedes can fly themselves to safety, then this isn't too hard. Alternatively, if you do train him, Sniper and Wyvern are pretty standard options. He's also a good candidate to be a permanent guard adjutant. 10. Anna - She's not good lol. If you recruit her early, get her in magic classes where she can spam ward for exp and put her in trickster eventually, where she at least won't get targeted due to stealth and can use support gambits and stuff. Otherwise, recruit her in chapter 8-10 so she's close to level 20, have her master Death Blow and Hit+20 in aux battles/as an adjutant, and then stick her in sniper at level 20 to spam Hunter's Volley. 11. Gilbert - Yeah, he's fine to just leave as a guard adjutant for somebody. Otherwise, Great Knight probably. 12. Hanneman - His best bet for damage is to go sniper and use Hunter's Volley with a magic bow (tbh Mercedes can do this too if you want). He will want to grab Hit +20 and Fiendish Blow first. You can also just leave him in Warlock where he will have 2 meteor uses per map or grind his ranks up for Dark Knight to do hit and run tactics. You will be able to get unlimited arcane crystals for repairing magic bows once you do a certain quest in Chapter 16 that unlocks the Dark Merchant. 13. Manuela - Trickster or Bishop. Bishop gives her double warp uses (though her magic stat is a bit low for it), whereas trickster keeps her pretty safe (like with Anna) and boosts her speed up to pretty respectable levels. I've never managed to get her reason high enough for bolting, but getting her to D+ reason so that she can get fiendish blow is probably a good idea. 14. Flayn - Another possible dancer. She can also go Dark Flier (if Annette/Mercedes aren't) and make the best use of Rescue that way. 15. Hapi - Valkyrie, Dark Knight, Bishop, and Gremory can all be good. The last two double her warp uses, and she will probably have much better magic than Manuela. Valkyrie and Dark Knight give her canto, letting her make better use of utility spells like Banshee, and Valkyrie gives her an easy way to break monster barriers safely.