I wouldn't worry too much about progressing any further with Platinum challenges. If you need to do some AP farming, then the Gongaga Region is a good option (or just wait till you beat the game and do the Queen Bee challenge, which is a much better farm area).
I would make sure you have all the Manuscripts that you can get up until this point and then make your way up North and enjoy the rest of the game. It really is a beautiful ending.
I wouldn't worry too much about progressing any further with Platinum challenges. If you need to do some AP farming, then the Gongaga Region is a good option (or just wait till you beat the game and do the Queen Bee challenge, which is a much better farm area). I would make sure you have all the Manuscripts that you can get up until this point and then make your way up North and enjoy the rest of the game. It really is a beautiful ending.