As often as you like. Dont make it a chore. Weekly is fine. I find myself feeding them whenever my scrap bin (kept in the laundry) gets full. Probably every 3 or 4 days.

Spread it out evenly. But its not important, the worms can move around the bin easily. I spread it out, but you could just put it in dufferent spots each time you feed. The only thing to think about there is if you have alot of the same thing, like 3 pounds of water melon or bad fruit, if you pile that in the one spot it might ferment or go rancid. Spreading it out limits this problem.

Cheers
Raf