Well, my normal routine for new BPs is, Get your husbandry spot on, and let the baby alone for a week, but since your baby is on the thin side i'd say only wait 4 or 5 days, so he can get used to his new home. For food i would try a fuzzy rat, that size is good for most small bps. offer a live, since its more probabul he'll eat that. Once he is on a 5 to 7 day eating and has gained weight, you can switch him over to ft. The most important thing right now is to relieve stress and get some food into him. Good luck