Good you got a UTH to up the hot side temps and that it's being controlled by a thermostat. To be clear, there is a probe for the thermostat attached, correct? It's not a UTH with, essentially, a dimmer on it, correct? If so, you still need to plug into your zoomed thermostat until you can get a better one down the road.
Nice work on the backdrop and identical hides. A happy secure snake is a good eating snake and, usually, at least with BP's, a pretty calm and docile snake.
Good question on humidity. It's up there in importance with temperature. Misting systems have pros and cons. A big con with them is that the mist is usually cooler than the air temp and brings down temps. Cold and damp are not good. They also need hydrometer to tell them when to run and to keep them from making things too humid or not humid enough. That's another cost.
I would recommend covering the top of the tank with tin foil (safer than a towel, for example, if you have a CHE, etc) aside from where the CHE is. I'd also look at your substrate. What are you using?
Make the tin foil as tight as possible over the screen and that will help keep humidity in.
Misting with a regular water bottle sprayer/plant mister from home depot for $1 can work, but don't overdue it, and USE WARM WATER. When it's a little dry in the winter, I mist my Boaphile tanks with my humid residents (BCI and BP), every day or two (as needed) but fill the water sprayer with hot tap water. Not boiling etc. But 110-120F tap water (thats about as hot as my tap water gets). Then I spray before it cools down. On mist, the water drops temp substantially when coming out of the spray bottle. 110F = 80F when misting. Never mist with room temp or cold water.
Another option is to use cypress mulch or Sphagmum moss, or a mix, over or mixed in with your substrate. A little goes a long way and can hold humidity well when pre-moistened (by you). You also put in a little dish, etc. to help raise humidity.
https://www.amazon.com/Zoo-Med-Fores.../dp/B0010OVM7A
https://www.amazon.com/Zoo-Med-Labor.../dp/B0019J2MA2
Keep us in the loop on your progress and continue to ask questions as needed. We are here to help.