Number one, the male rat will NOT kill the babies. He won't really help in the baby raising process, but he will not maliciously kill the babies. That won't happen.

He will however rebreed the female right away. This means that you will be pulling babies at 21 days old and force weaning them because the female will be constantly birthing new pinks.

If you only have one BP chances are that he will only be eating 2 rats per week at most. This means that one litter of pups will last you at least 5 weeks. You will be freezing off your baby rats when they reach the appropriate size.

I think the most cost effective way to do it would be to breed 10 females once a year and then freeze all the babies when they get to the appropriate size.

To answer the question that you asked, two females will be more than enough to feed your one ball python.

I would however separate the females when they are pregnant, not because the male will kill the babies, but sometimes the females will try to steal eachothers babies and they will inadvertently injure and kill some babies occasionally. My baby survival rate goes above 99% when I separate the mommas. About 85% of the babies survive when I leave them together.