If there is a lumber yard in your town ask for prefinished asian birch. I used the good one side (G1S) and will paint the exterior. The finish on the plywood is a 2 part epoxy that is baked on. I build custom cabinets and that finish has held up to everything.
As for the heating I have had no trouble with heating pads on the wood. I am about to start a set of 4 stacked cages for my brother and his boas out the same material with sliding doors.

Hes my burms cage: