I've seen your story of this snake so I want to say, careful not to overfeed it. Just like humans, after being underfed a snake can die from over-eating. You have to make sure you work it up to its normal size prey.

I think you should wait more than 2 or 3 days between feedings, maybe like 5-7 days. I don't know what to make of your current prey size. There's not really a good way to tell how many large mice = a medium rat to my knowledge. I would guess if you have to give 3 mice per feeding. It might also be a good idea to start on small rats for a couple weeks before feeding medium rats. Measure the girth of the snake and the rat too, it's a lot more reliable than eye-balling.

Hope this helps, and hope if I made any mistakes someone with more knowledge will be able to correct me.