Glad to hear he went. :) When I first got my girl, she was somewhat constipated, probably due to stress. Now I've had her for almost a year and she just went about 3 weeks without excreting. That was after a fast. Anyways, they have really weird bathroom habits, so I wouldn't worry at all. Sounds like you got all the temps going great, good setup, good feeding schedules... your buddy is probably a very healthy, happy snake.
Rats are more nutritional than mice, since they have bigger bones, meaning more calcium. So if he's big enough for rats, that's what I'd go with.