For what its worth I would start with a bag of 20 frozen appropriate sized rats for feeding. After it has consumed 10 rats weigh it and adjust accordingly for your next order. If you are feeding pups 10-15% of the weight of the snake on a 5 day basis it will definitely be ready for the next size up when the time comes for placing another order. At this rate you would go through 6 pups in a 30 day period so it would take about 3 months to feed off the bag of 20 pups. As I am not a fan of waste I would feed the entire bag even if the snake has outgrown the meal. It wont hurt it to be fed a pup every 5 days for a few more weeks until a larger meal is offered. In which case it may go threw a nice growth spurt when you do feed it a bigger prey item!