Temp probe for the hot side goes right on the glass above the UTH.

An aggressive snake probably means that he is stressed or feels unsafe. Try getting some tighter fitting hides. Sounds like you have a tiny baby on your hands.

It really isn't necessary to feed in a separate enclosure. You can feed him in his home enclosure with no problems.

The cardboard on top will just absorb the moisture, you want something that will keep moisture from exiting the tank. Plastic wrap or tin foil work well.