Wow! That's a lot for a snake in a single week....even one that's as active as a garter. They can be total pigs and will just gorge themselves. For a 32in. snake I'd think that a nice sized mouse (say a small adult) or two good sized fuzzies are enough OR say four nice sized goldfish (or other fish of approx. 2+in.) twice a week should be enough. The thing with mice is since they tend to have more "fat" to them, you don't need to feed quite as much. My 24in. male T.s.concinnus eats on good sized fuzzy once a week and is in very good health and shape. As far as supplements, yeh, the mice will do it, especially if they been raised well on a good diet. Only if the snakes are somehow going to be "stressed", like before breeding or something, will I supplement even with mice and even then it's only once a month.