Pretty much anything else a chicken eats. I have read that they should get less corn and more in the way of Vit. E. Mine have not ever really liked playing with whole apples or pears i put in with them but they gobble up cooked spaghetti noodles pretty fast.
Yes it will, and it will be big enough probably for a long time.
Silkies don't take up much room and the fancier they are the less the move around it seems.
The pet quality birds run around like regular chickens but the heavy crested birds don't travel much [too hard to see and they get lost easy!]