Glass is not a perfect conductor so there will be a difference between the t-stat probe and the thermometer probe. You want to set the reading on the t-stat so that your thermometer gives a reading of around 90*F on the surface of the tank. It will vary for each setup. For instance, on one of my hatchling racks I have to set the t-stat to 98*F to get the tub hot spot to 90*F, while on one of my adult BP racks a t-stat setting of 85*F yields a 90*F hot spot in the tub. I would also suggest a backup IR thermometer to get a true surface temperature reading, as the air temperature may be affecting the thermometer probe.
I take it out. Mine is held in place by the hide. Sometimes the snake moves it, I just put it back.2. Kind of a dumb question, but when you do in-depth cleanings do you remove the thermometer probe, and if so how to you re-stick it on to the tank floor? Or do you just clean around it and leave it stuck on?
I haven't noticed much temperature difference with the fan off versus on. It can hurt your humidity if it ends up forcing more air exchange in the tank though.3. Has anyone found whether using an overhead fan will force them to re-adjust lamp power or thermostat temps or anything? I'm sure I'll figure this out with time, but I was kind of curious, as my tank is in my bedroom and I run the fan sporadically.
Can't help with the lamp, perhaps try rigging a holder from a wire clothes hanger?