I always try to figure conservatively so my assumptions are:
Each 1.3 colony will produce approximately 3 litters per month and each litter will average 10 kittens.
Therefore each 1.3 group will produce approximately 30 babies per month.
Once you have grown them up to full size (unfortunately that takes about 9-12 weeks!) each adult rat should be in the 75-90 gram range. Your ball pythons should be eating about 15% of their body weight per week so now you just have to do the math ;-)