1. Aspen is great if you are looking for something attractive and easy to spot clean. In my opinion, newspaper or paper towels are best because when you clean, you just pull the old out and in with the new. I also like them because your snake can't accidentally ingest any substrate when feeding.
2. I'm not sure what brand it is, but a lot of people have a thermometer from Walmart that measures two temperatures and humidity. I think it's an accurite? Someone will correct me if I'm wrong..
3. Just make sure you have at least 2 identical hides, one on the cool end, one on the hot end. If your tank is large, clutter it up with branches, lots of hiding places, foliage, etc.
4. If you're using an under tank heater for your heat source, make sure you get a thermostat. The heat pads can and will get way too hot and burn your snake.
Can you post a picture of your setup? It would make it easier for us to give you advice.