A. You can make that tank work. You can even make the 40 gallon work. I raised my ball in a 40. The key is drift wood, plants, and hides.
B. It sounds like you have a dinner and not a thermostat. That to can work but if the room temperature fluctuates much througout the day and night the temps in the tank will be riding and lowering constantly. A steady room temp helps.
C. Placing glass over the screen will really help humidity a heat.
D. Heat mats are not meant to great the entire enclosure. They are meant for a hotspot. If the room is cool you may need to add a lamp or che.
E. Herpstats are king in the world of tstats to me. I had a Hydrofarm and it failed within two months, in the on position.
F. Get a IR temp gun. It will save you a ton of stress and really help you get things right.