Hi again Jess,
Generally speaking, babies need about 2 and a half ozs per lb of body weight per 24 hours. So he's probably about 9lbs now, and that works out as 22-23 ozs/24hrs. If he's having 7/8 feeds of 4ozs that's 28-32 ozs in 24 hrs. It does seem quite a lot, but babies aren't all the same. Are you sure he's really hungry after a feed? If he scoffs it fairly quickly, it may just be that he needs more sucking time. That's when a dummy can help (or a clean finger)
The difference between "Premium" and "Plus" is that the first one is made from the whey part of milk, and plus has more of the curd part (casein) This protein is more difficult for babies to digest, so they usually need to feed less often, but it's harder work for their digestive systems, so not really recommended for newborn babies. See what your HV says.