Id wait till you have the mite problem under control with a product such as Provent-A-Mite. Give him a week at least to settle in. And offer a rat pup.
If he hasnt eaten you definetley dont want to stuff his tummy. But once hes eaten a few pups for you, you can bump him up. Aot of people like to feed bloods a meal large enough to leave a small bump in the belly up until a year old. Increasing food size accordingly.
Subadults get fed once a week to every 10 days. Adults can get fed ever 10 to 14 days. Some will even feed once a month.
If this helps I'm feeding all my bloods 1 medium rat a week. And I have a 12 pound male, a 7 pound female, and 5 pound male.
Hope this helps.