Am I doing this right?

[micharoo47]

Hello everyone! I just got a young ball python (the previous owner wasn't sure of the age but placed her between 2-3 months) and I wanted to make sure I have everything set up the way she needs it. I got her and her tank as a package deal so I'm not sure as to some of the exact details because those were set up by the previous owner. Here's what I have:

-20-gallon glass tank w/screen on top
-brown wood-like substrate (looks synthetic)
-half-log hide
-3" water dish w/ good water from MOM's
-UVB light, 75 watt daytime heat lamp w/metal shade, 75 watt blue nighttime heat lamp w/shade; all 3 are 12" from the base of the tank
-spray bottle (used once daily) for humidity
-frozen fuzzies
-1 beautiful snake!

I also have a heating pad I was thinking of putting under the tank to heat it up a little because the lamps are 12" away and it says on the boxes that that means it will be 68 degrees (night lamp) or 86 degrees (day lamp) and that seems too cold based on the Caresheet.

The previous owner had her on 2 live mice a week and she's pretty big already- I want to keep her kind of small while still being healthy, so I was thinking of taking her down to one F/T fuzzy a week after she gets settled in.

She is still in the same tank with the same setup she grew up in, and she seemed very curious (nosing around the tank, especially the top) when I brought her home so I took her out the first two days and played with her for about 30 min. She seemed to love it; she was exploring, going from hand to hand, and being very active. However, today when I tried to take her out again she bit me. I made a rookie mistake and held my hand in front of her face (I thought she wanted to climb onto my hand rather than have me pick her up) and I think she thought it was a mouse and struck. Her teeth barely went into my finger though, it barely hurt at all and she drew back super quick without holding on at all. Was she trying to warn me to back off, was she hungry and mistook me for a mouse, or is she irritable for some other reason, like too much handling or bad conditions? Should I have waited a week for her to get acclimated (even though it's the same tank) before trying to handle her?

Her eyes are also a bit cracked-looking, but I assume those are just caps that will come off during her next shed.

My questions are as follows:

-should I set up the heating pad and where should I put it- under her hide (but still outside of the tank)?
-is it okay to use tap water in the humidity spray bottle, and is this even the best way to keep the humidity up? (I'm a broke-ass college student so if it's not, low-budget suggestions would be appreciated!)
-will she be okay eating only one mouse a week?
-why did she bite me?
-is it okay to pick up her hide to take her out?
-is MOM's water ok (it might be filtered)?

Thank you so much for your help and advice!!!