Quite true--only reptile mites will feed and breed on reptiles. Mammalian mites will not. Mite products are very toxic, so never expose your animal to any medications or treatments unless absolutely necessary. Never as a preventative.

As for prey sizes--you refer to your snake as 'he'. Male ball pythons are generally smaller than females as adults. The adult sizes of different individual ball pythons can vary from 3 feet and 1500 grams (or even less) on up to 6 feet, and over 4000 grams for enormous females). Both ends of this range can be healthy animals that are well fed.

If the rat is as big around as the thickest part of your snake, then it's the right size. Feeding a rat that size every 2 weeks for a non-breeding snake should be absolutely perfect. A ball python that goes off feed for 4 to 6 months over the winter should probably be fed every week while it's eating, but if it eats year-round, every other week is best. Since snakes rarely eat while in shed, just skip those weeks. This should keep its weight up without allowing it to become obese.