I dont churn out babies every 3 weeks, and it takes longer to fully wean the pups anyway, so I keep 4 females and 1 male, whom I replace every 12 months, also I replace the females as they get old and too cranky, as rednut said, they bite very hard.
I keep mine in constructed wire cages, i made them in a tier system with slide out trays underneath that makes cleaning very simple, a bit like a click-clack rack but made of 10mm welded mesh. The wire also ensures good air flow keeping them cool on hot days. Rats easily succumb to heat. By having a number of females I have the option of removing a few pups from each litter at various stages to ensure continous supply of approriately sized food for my snakes. I have 8 snakes ranging from 1ft to 10ft, I still need to supplement their food with chickens and chicken necks.