I'm rather new myself, but I do think the thermostat is a bit overkill for just one snake. There's very reasonably priced digital ones available that work very good with the heating mats, but if that's what you want, don't feel like you shouldn't buy it! RE the tank size, balls get stressed when there's too much space. A large tank is fine for a young ball as long as they have plenty of hiding spaces and cover and not a ton of open space. This is the thermostat I bought, but there are more that are mid-ranged, this is on the cheaper end of the price scale:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

I'm still working on the heat and humidity thing myself, but there are tricks to up the humidity... Use coconut fiber bedding (holds moisture better), put tin foil on top of the cage (also helps with heat), if you have an overhead heating source put the water below it, get a bowl of damp moss in there or make a damp hide for the snake to go into when it needs to, things like that.