5 oz is a very good amount. Eating often is not uncommon, some just have it that way and I don't think it is snacking. My Anna also nursed often, 7-9 times in 24 hours, and I was OK with that.
Yes, when they get older they nurse faster and are able to express more milk from your breast than when they are little. I think your little one is doing wonderful, think of all those moms who get 2 or 3 times a night for a quiet and cozy feeding :lol: .
Have you been comfortable with your breasts since he started to sleep through? Many women report getting engorged because of a long stretch without feeding and some even wake to pump a little to relieve it.