What do i need to know to breed rats?

[Bubbles]

I want to breed rats and plan to keep them all(I have 5 cages that will hold 5 rats each and 3 cages that will hold one rat each)I'm not going to breed without doing my homework though, and i want to breed two litters at the same time incase i need a surrogate for one litter but other than that what do i need to know?Thanks