I too use the homemade spray booth and have thought a lot about ignition sources.
Box fans are not to high on MY risk list, they are a brushless motor- so no sparks from a commutator & brush assy.
Blades are plastic so no risk of sparks being generated there either.
IF a bearing were to fail then there is a risk of sparks.
BUT- the switch sparks every time you turn it, set it where you want and leave it alone.
Connect your fans to extension cords that are plugged in somewhere else outside of your booth.
Plug and unplug the cord at that location to turn the fans on and off.
Lights: I use auxiliary fluorescent lighting, the risk of sparks at the connection of the ends of the bulbs and the sockets is a concern to me.
I make sure there is no corrosion on either, then I apply some dielectric grease on the contacts before installing the bulbs.
I only spray a couple times a year, so I check and service them before each "booth setup".
I plug my lights into extension cords and do the same as the fans, plug and unplug from outside the "booth"
Air compressor: big risk - keep in another area, there are pressure switches,metal pulleys,magnetic starters, etc.
Needs to be in a remote location.
( not to mention it might be blowing oil vapors into your booth air)
Thermostats, the old contact type are a spark risk.
Solid state not a problem normally.
If either were to short out and burn up they may provide an ignition source.
I turn off at power source.
Garage door opener: possible source, unplug it.
Light switches: Danger Will Robinson! they arc internally darn near every time you turn them on or off. I turn them on before starting and do not turn them off until my "booth" is totally cleared out.
That is my routine, not saying it is safe or unsafe, just my thoughts for my "booth"