First few feedings, leave him alone for 2 days at least.
After that, you can check on him, but as AbsoluteApril said, aim for about the girth of the body and you will be fine. I get scientific and if feeding 7-8% of body weight, doubt there will be much of a bulge. It's when you start pushing past 10% that you risk that, IMO.
However, I will defer to AbsoluteApril since she has taught me much of what I know about BCI's.
Regarding hides, Behira uses them sometimes, sometimes she half uses them (tail and body in and head and neck out), and sometimes she doesn't use them at all. She's certainly not shy or timid like a BP. Very different personality both in and out of the tank. Boas curiosity and inquisitiveness tends to outweigh any fear they might have. As they get bigger, fear seems to go out the window.
My BP is almost always in her hide unless hunting. Same with my corn snakes. Behira, eh, she does what she wants.