I have my breeding group of 4 adults and 3 sub adults in a 30 breeder, with a few blue rams. I used to have 6 adults in a 20 long, and only upgraded when they started breeding. You are right, they are not very territorial but I would try to minimize number of males. I think the best is to get as many young ones as possible from different sources, grow them out, then when they are sexable and if you are overloaded with males, start selling some. Not everyone wants to breed them, some people just like how they look and might want a random one or two just for their collection.
My adults are all wild caught. So far, my male has bred with 2 different females and produced 2 spawns. The young seem very healthy, I have had more losses of regular bristlenoses than leopard frogs! I don't do any changes to my water, it's just city water. Guess I was just lucky.