Taken in order your questions:
Maintenance for a resin printer means keeping the vat or tray clean, using appropriate methods to remove the unused resin (or leaving it in the vat per manufacturer's directions). Cleaning the tray should be done also per manufacturer's spec, although each printer's user forum may provide better or more effective options.
The Pegasus Touch has a caution regarding dripping resin on the mirrors, so there's operational care considerations for these types of printers.
There is a build platform for these printers. The flatness and level are as critical or more so for resin printers, as the resolution can be astonishingly high. If any portion of a print does not bond to the platform, that entire print will have a failed section, creating an entirely failed print. Gravity is not particularly helpful in that respect, at least with the Pegasus Touch.
The release medium varies from device to device. The Pegasus Touch originally used PDMS (silicon release compound) and now uses what's called a SuperVat. The plastic material in the SuperVat is purported to provide better release and fewer failures, along with increased lifespan. PDMS becomes cloudy from repeated printing in the same location and can be torn away from the vat if the print does not properly release.
I've become aware of a product from Australia that has had good reports from use in a B9 Creator resin printer. The report indicates that it releases the model quite easily and barely turns cloudy. I have an order pending for this material, as I am hopeful it will perform as described.
The mechanics are also varied. One expects a system to raise and lower the build platform and to direct the laser or illumination system (DLP), but generally, this type of printer is somewhat simpler mechanically.
Because I live in a hot humid climate, my Pegasus Touch remains in the box, and my brain is about to explode with what I've learned of using it. Environmental conditions are likely to vary with different machines. I've seen references that 70 degrees F is too cold, others that say 70-75 degrees F is just fine, anything higher is too hot. Another user says that 65 degrees is good. The type of resin also becomes an important factor for environmental conditions.
The laser will create heat in the resin, so I'm inclined to believe that cooler is better. Different colors require different durations of laser light, somewhat akin to various plastics having different temperatures.
supports and overhangs are important considerations in an SLA or DLP printer, just as they are in FDM.
Expect also that many of the resin printers require that the user purchase only the product provided by the manufacturer. This isn't necessarily a negative as most of the resin sources are priced similarly.
If I've missed any part of your question, let me know.