Sounds like you were in the right place at the right time for this little guy. I'd wait a week and leave a rat pup in with him overnight. Also, I agree with West Coast Jungle on the 5 day feeding schedule. You don't want to give him too much after being underfed for so long. Also, I didn't see anyone else say this, but I wouldn't handle him or mess with him at all until he's eaten for you a few times. Good on you for taking him in! Hope he does well for you!