Hi, I'm new to the world of owning a snake and i have more questions than i thought i would.

I guess to start, I had assumed that the original owners were pretty knowledgeable, but based on the feedback my few snake owning friends provided, the cage and supplies they passed on to me leave a lot to be desired.

What he has now is a 20 gallon tank with a heat rock, a branch, and a water bowl. The top is ventilated.
From what i understand i should ditch the heat rock for an under the tank heater and establish a way to keep humidity in and keep a warm to cool gradient.
- What kind of under the tank heater should i buy and how much will it cost?
- how do i measure humidity and keep the tank humid enough?

Also, they gave me the rest of their aspen wood chips and that seems like a weird substrate. Should i be using something else?

Thinking about all the changes that need to be made also brought to light a bunch of other questions for me about the snake's health and happiness.
- Is it stressful for t he snake to have things moved around, added, or taken away?
- The snake has no hides and seems to enjoy hiding inside shirts and hats while being handled. Can i use a beanie as a hide/hammock without posing safety issues?
- what should i look for to know if my snake likes or dislikes the decorations or items in his tank? Is he happy?
- once all of his necessities are taken care of, i'd like to decorate his tank in a unique and creative way. Are there any materials that i should avoid or any i should definitely include?

I like to keep my animals h a ppy, safe, and pretty damn near spoiled so any advice at all pertaining to my questions or just anything you think i'm missing would be greatly appreciated