I hope you'll give us an update on him now & then- we love a "change of scenery" around here -especially such gorgeous "scenery". And questions are welcome, always.
Oh, while I'm thinking about it- one reason to size up on rodents for growing snakes is that more mature rodents are more nutritious- they have more minerals (to build strong snake bones) & more protein- whereas "baby rodents" are either "watery" with little nutrition (that would be "pinkies"), or they're higher fat, because they're still nursing (that would be "fuzzies").
Also- your snake doesn't appear thin in that photo, but some snakes sort of hold their breath in when stressed (as when photos are taken) so it can be hard to assess their body weight & condition from just one photo. But if he normally looks like he does in that photo, then I'd say he's in decent shape. But yes, for the sake of his nutrition (more minerals & protein), gradually sizing up his prey will do him good.