I'd just stick to one male. Males stink and are larger. I have 13 female-1 male and have plenty full healthy litters although just a few get to hopper size as i really just need pinkies and a few hoppers, weeners. BTW I keep a few rats together in a 20 g ( going to add a topper soon)and about 8 in a double layer(added a topper), 35 g tank. I have been blessed though as my rats are all undersized by genetics( all 4 starter female rats were small ).