Hi there!
1) No, I do not use hygrometers. I keep the water bowl in the rack and I have not had an issue with sheds ever. I also use paper towels.
2) Depending on what the humidity is, I'm not sure you need to mist at all. If it is too dry, you can just mist the sides. If you over mist (too high of humidity), it could be bad for the pythons (such as scale rot).
As for substrate, cypress and aspen work just fine, pick whichever you prefer![]()