LuLu, Manta Ray, mbear and the girls have given you some excellent advice!

Your bubba sounds perfectly normal adn healthy to me...they are milk guzzling machines at that age! lol
Also, at night they will tend to 'cluster feed'. So over the space of only and hour or so may have 2-4 feeds in that time, so that may explain the waking 5 mins later for more milk.
Try and go with his flow, offer the breast when he is hungry - babies that age will not let themselves starve, nor will they 'overeat' - they will naturally stop when they are full and feed when they are hungry. All you have to do is offer it and he will decide what he wants

So although it is hard going it the early days, lay off the expressing and formula - dad can help by feeding bottles of expressed milk in a few more weeks. Also, have you considered co-sleeping or partial co-sleeping? it may help with your sleeping if you can snuggle and feed in bed a bit together too.

I still think the best advice I got with a NB was to spend a good 2 days in bed with them. Stay in your jamies, leave the dishes and let DH cook dinner and spend the 2 days in bed snuggling, feeding and getting to know each other a bit - and getting to know his rhythms and his feed cycles, how and when he likes to be burped and which position he likes to feed from etc...

Anyway, you are doing a fabulous job! Trust your body to nourish your bubba - it know what it is doing