As far as whether to feed mice or rats, with Kings, I've always fed mice, but Django gets a very occasional rat (refusal from BP or Borneo) as long as it's a really small "small".
As adults I feed prey items that are the same size or a touch larger than their bodies girth every 7-10 days. Django has been on that diet since I got him 2 years ago and is still growing slowly but consistently.