Please get yourself a digital scale (walmart sells them for $15). Telling us length doesn't mean much when talking ball pythons. Weight is far more accurate way of measuring your snake. Your snake should be fed 10-15% of its body weight every 5-7 days, as a general rule. Rats are more nutritious and switching a mouser to rats later in life can be a real pain sometimes, so it is generally advised to start your ball on rats asap (most of us start them on fuzzy rats right out of the eggs).