There are plenty of awesome sticky caresheets on this forum. They can tell you about proper thermostat use, and if you still have questions, people will be happy to answer them for you.

My personal recommendation about a cold room, keep the enclosures away from outside walls, and if you need to, warm the room up with a space heater! I have my lovelies in the living room, and can maintain good temps in their tubs when the room is around 70-72. Ventilated tubs hold in heat and humidity very well. Another suggestion I've heard is to attach insulating foam around 3 of the walls to help hold the heat in, if you're using a glass tank.