Those insects and critters won't harm your monitor. Most of them are there to feed on the scraps of food, waste, and other little things in the dirt. It makes for a nice system. Toss in some crickets and if they last long enough they will lay eggs in the dirt and you will have little crickets in there for your monitor to pick off on occasion. Not nearly enough to make a dent in feeding but an easy perk nonetheless.
As for excess moisture, it really depends on what you are calling excess. You don't want your monitor swimming in mud all day. However, if there is a good temperature range and some ventilation, you should not have a problem.