How can I keep my humidity up? Follow the above mentioned tutorial. I use foil on top of my mesh top with it just crimped under the edges and it holds just fine without tape.
What kind of mulch or substrate is best? Depends on preference. Mine is cypress to help with the humidity. NO PINE or CEDAR, the oils can be toxic.
Is it better to feed them two fuzzies or one larger mouse? Is there anything better to feed them? One meal is always better, both money speaking and for the snake. Rats are the better choice if you can manage it.
Do BP's like foliage in their housing? I have a fake branch for mine to climb on, which she sometimes enjoys. But ultimately it is about security, if they need more to feel safe add what you need to.
Is having two hides necessary? I consider 2 hides to be necessary. One on the warm, one on the cool side. So you snake can thermoregulate it's temperature itself, with no discomfort.
Are all BP's head shy? Not all are, and mine was super head shy but she's slowly getting over it cause I kiss her on her head sometimesand just because I handle her alot.