Kaorte's input pretty much covers it. Just remember ball pythons are not all about having alot of space, it can stress them out. If you decide to keep the 40 gallon at least get a few more hides for you BP, Some under the light on the warm side and some on the cool side. Even if it seems crowded in there you BP will be happier being able to change hides if he wants to be warmer/cooler.
You could lose the light all together if you want also, they don't need any special light and it really does make it harder to keep it humid in the tank. A under tank heater is all you really need, you just some way to control the output of the heater so its not going full blast all the time.