1. they will eat ANYTHING but I feed mine algae wafers, bloodworms,
brine shrimp, and tetramin flakes...pretty much they eat whatever im feeding the others ...super bottom cleaners..as well as come to the top if they are impatient for things to fall
2. mine are in a 55gallon and yes I think 50 is great...
3. I have a rainbow in mine...the pictus stay on one side and the rainbow has his house on the other..I have no issues with them at all..not that I reccomend it, but if you check my aquaruim info, you can see whats in my 55 gallon with them...and everyone gets along... EDIT: ( which isnt the rule of thumb on those combo's)!