Hi,
Basically the most important things you need to know about your enclosure are security, temps at various areas, humidity and how the snake feels about it.
The acurite weatherstation with probe that costs about $12 from walmart will tell you the temp at the base unit and the end of the probe and the humidity at the base unit - so it is invaluable when dialing in the tank.
The thermostat is designed to regulate the heat pad to make sure it keeps the temps at the right level and avoid either burning your snake or keeping it too cold to thrive.
There are a few options ranging from the zoomed 500R at about $25 to the more trusted units like the ranco and johnson themostats at around $75 - $85 ( I think ) up to the cream of the crop proportional thermostats like the herpstat and helix for $110+
The good thing is thermostats last a while and can be moved from enclosure to enclosure as you upgrade etc. so it is a good investment.
They can also control multiple heat mats as long as they are the same size and the total wattage does not exceed the thermostats limits.
Have a read through the caresheet and see what other questions it brings up.
dr del