What are some signs that your bp is still hungry, and subsequently, how do you tell the difference between searching for more food and trying to get comfortable?

What's the best size to feed F/T if your bp is between a quarter and a half-dollar size at its widest point (we don't really have a scale yet, and picked up some mice that were too small so we had to double up. Would rather not go through food twice as fast )

Also, how many of you feed in the viv and how many feed outside? I've heard from both ends that either one is the right way to do it, so I'm just curious (because feeding outside then moving is a bit of a pain but if it keeps my fingers from being nibbled on when I try to hold him, then I'll do it).