You can cover part of the screen on top of the tank to keep heat in. Stacking the books might cover enough area to keep some heat in--have you checked the temps with the books stacked on top like you're going to when you use it? I'd go for some clips on the screen too.

If you haven't gotten the snake yet, consider getting a female. Most of us who have ball pythons eventually get bitten by the breeding bug. Having a nice sized female raised up when it happens is a big plus.

Everyone has their opinion on whether or not to feed in a separate box. I don't because 1) I'm lazy, and 2) because they eat just fine in the box they live in.