you want at least two, so they can keep each other company and they like to play with each other. (Not in the rude way) lol
I feed mine on a good diet of proper ferret biscults and roar meat, chicken wings & legs. also give them an egg now and again.
I keep mine in a 3 tier hutch that I made. this is when i first built it, looks a bit tatty now tho. lol
MTT.