On your substrate question, I use aspen in most of my tanks. I prefer the type that is small pieces rather than the shaved pieces. The small pieces tend to pack down really well and it is very easy to spot clean. Give it a shot and see how you like it.

As for the thermostat, the Zoo-med one is better than nothing however I will always recommend one of the more expensive ones since can actually set the temp by number instead of by the dial. For the one you have, you'll need to attach it to the cage (to the poster is fine, just let the glue for the velcro cure for awhile before sticking the thermostat to it). You'll then need to set it somewhere in the middle and watch your temps on your thermometer. You will probably need to set it just a bit above the middle to get the right temp.

If/when you get enough to buy a Ranco or Helix/Herpstat, you'll find it much easier to use and much more accurate.