1 Will they need different food? Im currently feeding mine Purina Flock Raiser cause I have a few that arent quite laying age yet but then I will switch to Layena crumbles when they are old enough.
Guineas need a higher protein than what's in the layer formula. I'm keeping mine on flock raiser, chickens and all. The chickens could use the extra protein too.
2 Will they hurt my chickens?
My older chickens don't bother my guineas. In fact they step out of their way and let them do as they please! The younger pullets however, see themselves as equal with the guineas and sometimes they will start a squabble with them. I've never seen the guineas start anything or be mean to the chickens.
3 Is just having two gonna be enough? Ive heard things about having a minimum.. or is that just all the enablers? 
Hehe... Well to be completely honest I think 2 is probably the minimum, since guineas are very flock oriented and don't like to be alone. (Just like chickens.) HOWEVER..... I'm partially an enabler too and would say get a few more... like 4. 
