As long as your heat and humidity are good, your tank set up sounds ok.

As a general rule of thumb, you should feed young ball pythons 10-15% of their body weight every 5-7 days. In order to do that, it really helps to have a scale so you can weigh your snake.

Once you know what your snake weighs, it becomes simple to figure out when to switch them over to rats. Rat pups usually run from 10-18 grams. When your snake reaches around 160 grams, it would be a great time try switching over.