1 & 2. Most people don't. Many people opt for using a temperature gun to check the hot spots in the tubs. You should have at least one digital thermometer/hygrometer to check the air temperature/humidity.

3. Tubs stay the same temperature as the air in the room. IF you have a completely enclosed rack then they might stay a few degrees above the room temp but not a huge amount. you need to keep the room above 75 degrees in most cases. but closer to 80 is preferred.

4. Either way works just fine it is totally up to you.