As mentioned above, you need a thermoSTAT. ALL heating equipment should be regulated by a thermostat.
Sounds like there may be a bit of confusion between t-stat and thermometer (could just be a typo?)
But either way, those dial style analog thermometers and hygrometers are unfortunately junk, so make sure it's a decent quality digital (I use Accurite brand thermometer and hygrometers. $10 at Wal-Mart)
Also, unless your room where the enclosure will be kept stays in the mid 80s you'll need an additional heat source, heat lamp + bulb or CHE (ceramic heat emitter) or a RHP (radiant heat panel). And remember, ALL heat sources should be regulated by a thermostat (I repeat this to stress the importance).
You'll also need a lid and an escape proof locking system. Snakes are escape artists and can be much stronger than you think as well as fit through places much tinier than you may think.
I've used MANY used fish tanks to house snakes. Never had a problem. I use bleach to clean though, then let the enclosure air out for a few days. There should be zero bleach smell at all before an animal is put into the enclosure.
Another VERY important thing to have before bringing any animal home is a stash of money set aside that is there for an emergency vet visit. Accidents can and will happen, illnesses happen, etc...and it's our responsibility as keepers to have vet money stashed away.
Good luck. Feel free to ask any questions you may have. And read, read, read and read some more. Learn from reliable sources and cross reference multiple sources before believing anything to be fact. The more we know about our pets the better we can care for them.