Hey!

1) I don't think its overkill because a thermostat is a MUST when you have an animal that requires certain temp so they don't get burnt. You can look for a cheaper model from VE or Spyder Robotics but even their lowest models should do what you need it to do.

2) I completely agree with being a 1 purchase kind of person. I bought a 40 gallon tank for my my first bp when it was a baby. the only thing you need to do it make sure you fill that space up with fake plants and hides so the snake doesn't feel in danger. and with a tank like that, keeping humidity will be an issue because of the screen top, but it can be done with some moss in the tank, some misting and covering half the screen with something like a damp towel or something like that. Heating will require a heat mat and maybe a ceramic heat emitter in order to keep the ambient temp where they need to be.

And you say you will only have one, thats what i said too. and now I have seven. welcome to the addiction! haha