Look this is just my opinion okay but if you are going to purposely breed any animal you need to have some concern for the female's health and a basic understanding at least of rodent reproduction.

If her body is burning energy to both grow developing rats inside her and put out sufficient milk for the care of her current nursing litter she's going to have to be either fed very well or those nutrients are going to come out of her own stores. In other words she'll can down hill, get skinny, etc. if she's both pregnant and nursing litters then constantly rebred. I know some people do back to back birthings and that's their option but I don't agree with it. No female animal in my opinion deserves to be bred like that.

I keep enough females that all my females spend the last week of their pregnancy in a seperate tank. They birth there, raise their pups to weaning age then go to another tank where they spend some time rebuilding their own body before being reintroduced to the male rat. This does mean I keep more females than some, and I don't produce the number of litters from each female that some do. That's fine with me I'm not trying to do production breeding, just to provide high quality feeders for our snake collection and do so in a way that respects the rats for their contribution to that end.