As long as you're tight, doesn't matter if they bulge out. Hell, that'll prob'ly happen anyhow.
As for the back, you'll be fine as long as you make sure you're in extension. If you're worried, record your lift and watch it, and if you're not sure, post a form check. While the belt will, in all likelihood, get you stronger, it won't protect you if you're trying to deadlift with a catback.