They probably wont eat flake for a start until they have settled in, besides, there are better things for them. Try frozen bloodworm or mysis shrimp
Depends on a variety of things, lighting etc
Yes
Many, as mentioned White spot is common when they are settling in, otherwise they are quite hardy but things always can go wrong down the track
Well they aren't plants so they aren't too fussy! A single T8 tube should be enough so you can see them, dimmer the better provided your plants have enough (this depends on what species you have) and you can see them, especially if you dont have a chiller
No they dont need caves
You havent said how many inaga you have!
dont use this as a preventative, clean water with stable parameters is much more important