We all started out sometime, so do not worry about that...the fact you are here to learn shows how much you care!

First of all..Ball Pythons can go off feeding for a long time and still be alright. So no worries there.

Once we see pictures of her, we can help you with the food size. It all depends on how much the former owner fed and how big the snake is.

If the snake was used to a rack/tub and is now in a cage, that can certainly explain her reluctancy to eat. That is a big change for her. There is a lot you can do to make a tank more private, though.you can use black contact paper (or other paper) on the outside of the tank to black out the sides and back. Then cover the top with foil for added privacy from above. That will also help with humidity. I don't think you will need a mister. That might end up stressing the snake out even more with that coming on every few hours.

You should be able to get the humidity up with the right substrate and keeping the top covered. As well as using the right heat source. Lights dry out the air as well as stress a snake that was used to more privacy.

You will get it all figured out. If the snake is healthy, she can go a long time without eating and still be just fine. You will have many more years with that beautiful creature. Just tweak the setup and the rest will work out ☺️