Re: too much milk
Some heat on your boobs can help soften them that or a little bit of pumping (not a lot - that can make things worse in the long run) just to help the feeling like you have boulders in your bra before having baby latch on. Your body will regulate supply as it figures out what he's actually taking.
He sounds fine. I think we as moms look for problems that aren't there. Follow his cues. If he seems happy doing that, he's likely fine.
And yes, you can nurse entirely on one side per feed, I've done that with DD2 since she was a newbie. I will warn you that you'll occasionally look lopsided when it's been a while between feeds, but that doesn't happen so much now that my baby is older.