You can offer anything roughly the size or up to 1 and a half the size of it's girth (widest part of it's body) every 4 to 5 days without any problem.
You can switch to rat right now, they are not picky eater they will pretty much eat anything (live, f/t, rat, mice) anytime offered.
They are garbage disposal
I would wait 2 to 3 days to let it settle and than offer food, than 2 days after that you can start handling your new pit.