1) Immediately seperate any boy and girl rats. They cannot play together, or even have their cages pushed up next to each other. Consider keeping rats of only one sex, or having males fixed. If you just got these girls, and they came home pregnant, you should call that shop and berate them for keeping their males and females together!
2) Start planning now to find good homes for every one of those babies. They are your responsibility. If you're considering a pet shop, think about how many of them will end up reptile food.
3) Make absolutely certain you seperate all the babies by sex by the time they're 5 weeks old or you'll have tons more babies
As for your questions, I'm not a breeder, but if you follow this link you can find many good articles on raising rats that may help you out-
