Size of the rodent meal looks just fine to me. Not too big nor too small.
And his body proportions look just fine too- keep doing what you're doing. (Except the ladder rungs, - snakes don't have hands to grab on with & they LOVE to find things to hang onto- they automatically crawl into & thru things because they afford "traction", & they don't seem to understand that at some point they'll get stuck- they evolved in a world without manmade stuff everywhere. In this case it looks like he could get his head stuck, & "if" it happened when you were asleep or not home, your beautiful snake could really hurt himself trying to get free- I'm thinking he could dislocate or break his neck...things best avoided.)