I raise ASF, Norway rats, rabbits, pigs........

First question is how many prey eaters are you feeding?

Then what size prey do you need?
For 10-125ish grams you won't need grow out tubs. Pull the moms at 35 days (weaned). I give the females two weeks off before I put them back in with the males. Some here an others I know just put the females back into the breeding rotation.

I say you won't need grow out tubs because by the time the females have to be removed from the males the old litter is ready to be gassed. Now, if you put the females straight from weaning to breeding you may want or need grow out tubs. For grow out tubs, try to keep the rats about the same size.

As for females having their own tubs.
Depends on the size tub used an the rats. "If" the males did their job the girls "should" drop around the same day give or take 24 hrs. Good moms are just that. Buttheads will fight to steal babies. Pinkies get hurt that way. Then you have the ones that if stressed will kill/eat pinks.

Using large mixing tubs I have an do let three females nest. These are the older breeders that haven't had problems. For the small tubs it's one per litter. If a first litter or any litter is small (6 or less), I spread the litter around an take the next step with the rat (keep or cull).

Cull any injured young. Or they will be eaten. Cull all nasty rats, no biters or fighters. Rats only live 2-3 years don't waste time. You have to add new blood from time to time. Dad breeding daughters an then breeding grand daughters messes with litter size an fertility.

Breed fancy rats! If you have extra fancy brings $$ pet money. Lab white rats not as much. I get $20 for blues any time I sell them, $10 is easy for a fancy rat.

I always put three females into the two males tub. Rule of two, one is none. Two males give better odds that the females will be bred an drop around the same time. Also keeps one male from getting attacked by three mad females I always pull the females out by day 17. In the 70's I left one male in with two females in glass tanks. The male would stress the females out always trying to breed while mom was taking care of the kids. Didn't take long to learn.

Now, starting a colony the easy way.
Find an old school pet store that houses all the rats together. The adult females are bred Find other rat (pet) breeders on face book an the like in your area. Trade or borrow a male. Animal shelters have rats, rabbits, snakes, birds an even horses. Check out your local ones.

Help full links(I hope):
miscsigl.vp (afrma.org)
Fancy Rat Varieties: Fur Color, Eye Color, Coat Type, and Markings - PetHelpful - By fellow animal lovers and experts
Building a Rat Rack (arbreptiles.com)

Good luck!