Sorry you're having a rough time. First, I'd like to comment on the supplementing as a bf'd lo is not necessarily hungry if they gulp down a few extra ounces of formula. You have to remember they are not used to formula or the free flow of a bottle because they have to work at bfing so when they are given formula in a bottle they tend to chug it down, regardless of fullness or hunger. Think of us adults eating a tasty desert after a meal when we're already full, to others watching they would think we are starved. As well, any amount of formula they take from a bottle translates to breast milk we will not produce as bm is on a supply= demand basis. I really do think adding formula to a bf'd baby that nurses well and gains weight appropiately does more harm than good.
If he's now taking a "10 min aggressive feed" it could be because he has become more efficient at feeding, he now knows what he's doing. I found the "milk drunk" look only lasted the first few weeks with my dd, then she became more aware of her surroundings. If you're really uneasy about how much he's getting is it possible to go and get him weighed before his next appt? It would give you peace of mind. When my dd started the fussing/bobbing at the breast I would put her one one side until she fussed, then to the other, until she fussed, then I would actually put her back to the first side if I was worried she didn't get enough and she would actually take some extra.
If he's having additional nws I would give in to the 2nd night feed, even if it's a partial feed (maybe just from one side). He's still quite young so it might just be a few weeks off that he'll drop a feed. I don't think you'll make a snacker with one feed that's not a full feed, to make a snacker you'd have to be feeding all day long the second he cries- one hour intervals, and everything in between and you sound like you're on a great routine for feeds.
Let us know how your next night goes and what you've decided to do.