Well the easiest way to deal with humidity for us was to just put a damp towel on top of the cage covering a third of the tank and yes your going to have to mist. Also keep a uth on a thermostat for your heat as a high wattage bulb will suck your tank dry. We keep two water bowls in our tanks one on the hot side over the uth and one on the cool side. As far as tank size go 40 gallon is a huge tank for a hatchling but you can always pick up a ten gallon tank at walmart for I think around fifteen dollars. Aspen will hold more humidity then you think but we use a blend of aspen sphagum moss and coco husk for all of our tanks. Good luck and welcome to the addiction that is ball pythons lol