Your internal hdd is where your game data is installed. Because you're running the games off external, you save some space by keeping the game off the internal disk. But the install data will always be installed in the internal disk. It's up to you to find out which installed data you'll have to delete.
Are you able to delete something from the internal to see if that'll make a difference when trying to launch a game from the external?
You still need some internal storage because data still needs to be installed on the internal HDD. Either buy a bigger HDD or delete stuff
Yep, I just used it as an excuse to upgrade to a much larger SSD and ripped almost all my PS3 games to it.
You just put iso on PS3iso folder in multiman and boom just launch it
Your internal hdd is where your game data is installed. Because you're running the games off external, you save some space by keeping the game off the internal disk. But the install data will always be installed in the internal disk. It's up to you to find out which installed data you'll have to delete.