I have had pregnancies as early as 2 months 2 weeks old.

You just have to see what works for you by trial and error on the number of tanks. Too many variables to really make a guess at it for your situation.... size of snakes, how many they will eat each week, genetics of your asfs and how large their litters are. Just get what you can afford and experiment. The experimenting with different things is the fun part!!!!