You CAN keep a colony together in ONE cage without ever having to remove a female. Removing the female simply ensures they don't get bred again right away. If you provide a high quality food, rats can easily be bred back to back with no ill effects on the females. I keep my rats in a colony of 1 male to every 4 - 5 females and have found that the females aren't always pregnant if kept together with the male. The males will also help a LOT with the babies... cleaning them, keeping them warm while the females go off to get food, ect.
IF you can afford the room and extra cages, feel free to separate them. Some breeders have several bins going at the same time with one male for each bin of females and simply rotate the male every 2 - 3 weeks. This provides a good rotation and easily provides a constant supply of rats needed to feed your snakes, without overloading you with tons of babies at any given time. The litters will be spaced far enough apart to allow you to feed off the babies in the first litter as the second litter is being raised, when they reach the appropriate size, you have finished feeding the first litter off and are ready for the second litter.
Be warned though, that you will have to buy food and bedding for the rats (I prefer wood stove pellets as bedding as it is very cheap and absorbs much of the odour). If you are having a hard time buying a few rats now, how do you plan to care for a couple of breeding colonies of rats?