I have 4 marble angel fish....2 breeding pairs. Beautiful fish. I love them. I think everyone should have angel fish at one point in time. they are quite the characters.
like others have said get 5-6 small ones and then watch them, some will pair off, and you may even be able to keep two pairs in a 55 gallon tank. Sell or even better trade the unpaired ones for other fish such as the oto catfish for algae control. I used to have angelfish until I traded them and I miss them, they are great to watch, and have a good deal of personality. if you are really set on angelfish Id recommend you find blue angelfish, they are a new variety. for a 37 gallon a fluval c3 is okay, but you'd probably be better with one C$, and you'd be all set if you decide to upgrade to a 55 gallon tank...
I agree with what the others said about getting 5 or 6. I have 5 in a 40g. 1 black, 2 half black and 2 albino. White r just as beautiful as black IMO. Angels move slow and r very calm fishes, so I suggest u don't put anything fast moving in there firstly cuz of the food and secondly fast moving fish desturb them and make their fins go down. If u want to see them with fins up more often go with slower water flow. I've kept them with dwarf gouramies and they did very well. Avoid any fin nippers!! they love angel fins. Good luck and hope to see pix of ur angels once u get them