Don't stress too much you're doing fine. Personally I would stick with rats and not do the mice, just incase he decides he only wants mice... in which case, they do not have as much fat in them and whatnot. If you can find f/t (or live, depending how you feed) rat fuzzies I'd start with those. That is what I feed mine, although he could go up to pups anytime - I'm just emptying out my stock. Mine was 116g when I got him, 3 months old, eating rat fuzzies.

He's gorgeous, by the way (yours)!! Best of luck.