I can't help here. I use tubs so I don't have any experience with moss. I assume you have a glass tank though and would sugggest covering most of the top so you retain humidity. Humidity should be 50-60%.
Your snake needs a hot side that is about 90 degrees. The cool side needs to be 80 degrees. If your setup has this temp gradiant then there is no need for additional heating sources.
See above but if it helps keep your hot and cool side temps where they need to be then it is perfect.
You need a temp reading from the hot side and cool side where the snake can actually be. That means directly on your substrate on the hot side and cool side. The hygrometer should be centered in your tank as best as possible.
In the states they sell simple digital units that read two temps and the humidity. I would recommend looking for one. For a referance picture you could look up an Accurite digital temp/hygrometer. I don't know if they sell them in the UK but I'm sure there is something similiar.
As often as is needed to keep your humidity at 50-60%.
Up to you but hiding spots are always appreciate by Ball Pythons.
Aspen is typically one of the better wood chips. You need to make sure there is no dust. I use paper so I can't help a lot here.
If you mean a thermostat, proportional is the best way to go!
Welcome to the hobby! You're off to a great start if you have come here to get some answers. Feel free to PM if you need any more specific help.
Regards,
B