We have 3 butterfly fish but one is seperated from the others as she was being chased a lot by them so be careful, ours are in a 300 litre tank with plenty of plant cover from long vallis but they tend to be a little aggresive towards eachother.
We feed ours a mix of foods, mainly a pinch a day. They love freeze dried bloodworms, dried daphnia, dried tubifex, and vitakraft special mix which has nice crunchy shrimps in for them. They will hand feed from a cube of frozen bloodworms as i feed the others too. They are really nice fish. Ours also tend to go lower down in the tank although i am not sure why. It must show they are settled though if they feel confient enough to do this.
We chop very finely cockle mussel and prawn for some other smaller fish like the elephant nose in there and the butterfly fish have learnt to take some of that food as it goes in too.
Hope this helps a bit
Clare