Hi mate, welcome to the forums.
The minimum size tank is a 20 gallon long aquarium (30" long * 12" deep * 12" tall). However, if you can go bigger, then that's better, provided you provide enough cover (artificial plants, climbing space, multiple hides etc.)
I keep my Corn in a 50 gallon (36" * 18" * 19"), with plenty of cover and he loves it.
The ambient air temperature should be between 78 - 82F ideally, but as long as you have one warm area that's between 80 - 85, and one cool area that's between 70 - 75, then it doesn't actually matter that much.
All the best
David