Everyone kind of says different things. I have heard often:
1) Wait one week to feed
2) Wait 3 consecutive and successful meals before handling (so depending on the age of the snake, 2-3 weeks from when you get them)
3) It's up to you but they seem to be less stressed in the enclosure - although not always the case. It can be easier for you, as well.
However, all of those things are negotiable and individual to snake and owner. I think the most important thing for ALL THREE of those questions is to keep an eye out for signs of stress with your snake, which can be a number of things. Basically anything out of the ordinary for snake/ball python behaviour (I know, very broad. I apologize).
Best of luck :)