If you plan on breeding rats for the good of the species (a responsible, ethical breeder) then you would need to mentor with a proper breeder first and "learn the ropes". They usually would set you up with your first breeding pair and help you with the process.
You need at least 3 generations of known genetic history with your breeding pair.
Then once you manage all this, before you breed, you make sure you have reservations for your rat babies...you do not randomly breed and then try to find homes...
generally breeders will only breed one or two litters a year (and using different rats) Most breeders won't breed the same rat many many times, good breeders won't. Your best bet is contacting a breeder on the forum and speaking one on one with them.