It could potentially produce unspeakable abounts of rats per week, but it would be inhumane. I suggest starting with one litter, giving the mother at least a week between pregnancies. It takes about 2 months for a female rat to be bodily mature enough to healthily sustain a litter, considering she is being fed right. And costs of food and bedding, and 20 females? All at once? Oh jeez... I think you should do some research and maybe think about starting off with maybe one male and two or three females.

This seriously something you don't want to rush into.