A single tub will work fine. Just remember rats are social animals. So that means you have to handle them daily when alone. After the pups are weaned or frozen put mom back with some other females an then introduce your male or males. Pull the females out 5-7 days before she should drop. Your litter sizes will probably do better in a single tub. My litters size average 10-12 in a 3 female tub. I have had females steal babies. An I did mess up years ago by putting one male in with four females. I pulled the male at day 14. The girls dropped pups about a week apart. That caused fights an I lost 20 babies. For feeder rats I'll put three females in with two males. They all drop within a day or two. For fancy blue rats or what ever color is hot this month it's a 1/1 pairing. But that's the difference between a $2 rat an a $10-18 rat.
As for the number of females you need. Keep some weaned females an breed them. You have an idea what size what snake needs. Weigh an freeze a litter when it hits said size. 10 correct size rats will last said snake # weeks or months. Once the freezer is full then you can down size or sell. If you have BPs hatching have some girl dropping 5-7 days after an another dropping at week two..... I have two new breeders burning my phone up for live pinks an fuzzies. The COVID messed up their supply.
I posted this before but it's still go info:
http://www.miceandrats.com/standrat.htm
https://www.afrma.org/
https://www.afrma.org/pdfposters/reprofacts.pdf
An I'm cheap. So I feed TSC Doggy Bag to the rats/ASF an use TSC wood chips.
Get a Vacuum sealer! I really mess up an used the one my wife had
https://www.foodsaver.com/vacuum-sealers/
I think we have 50 snakes right now. I have six snakes that are mine, I've had them longer then my kids. Number changes as the kids will find more, rescue more an trade. Daughter came home with the teachers BPs last week. Poor things have been taken care of since March.
As for BP, I raise an feed African Soft Furs. I like them better then rats, well after you cull two/three generations to get rid of the biters. Never had an ASF outgrow a BP. Another reason why I like ASF. Tubs always has babies.
If you raise rats an BPs you need a rat snake or two for all the refused meals.
Good luck!