Things to take in consideration
You need to be able to produce without interruption
Rats produce between 6 to 12 babies per litter
Gestation is 21 days
Females will go through the following stage breeding, gestation, nursing.
A good rule of thumb is to have 1 female rat for every snake you own, if you have surplus euthanize them and either sell them or feed them to your snake that will take F/T