1. Will my snakes become ill from not having belly heat for a few days if I use a heat light in the mean time?
No. Many keepers use only ambient temps and their collections thrive just fine.
2. Should I just plug in the UTH (zoomed brand) and put like 4-5 inches of cypress mulch ontop to try to make it less hot?
No. The uth can not push heat through 4-5 inches of substrate. The proper depth of substrate is about 1/4 inch. If your snake is seeking heat it can burrow and find the uth. A uth covered in 4-5 inches of mulch will be insulated and the temp will be way to hot and put your snake in serious risk.
And as for the humidity...
I use cypress mulch, and have sphagnum moss throughout. I also mist 3 times a day and still can't get it to stay where I need it.
Your humidity does not need to stay high at all times. My ball is in a glass tank and the humidity stays in the 30's. I combat this by placing moist moss in the hides. This creates a humid hide that the snake benefits from directly since that is where it stays most of the time.
Today I bought some Eco Earth and a small one room humidifier to see if that will help. After this, I can't seem to think of any other things to try.
I use a mix of cypress mulch, eco earth, and repti bark. Mainly I do this because I like the look as I keep naturalistic tanks. It is good for helping humidity though.
I've been reading about wrapping the screen tops in everything from plastic to aluminum, but with my UTH not plugged in, I'm afraid to run a heat lamp ontop of plastic or foil.
I have a cardboard cutout on top of my screen. I wrapped mine in foil and cut out a window for the heat lamp and che heat to pass through the screen and warm the tank. I also recommend using lamp stands. They are about $20 at the big box pet stores. This allows you to suspend the lamp or che above the screen which keeps the hot bulb or element from touching anything, which is much safer. This also keeps you from moving the heat sources around which will prolong the life of the heat source and the heat is continually pumped into the tank instead of being removed while getting into the tank and having to remove the heat source from the tank. I have a che that has been working 24/7 for almost three years now.