One thing I always recommend it to upgrade the filter to the max. I run a 5 inch thick HEPA filter (MERV 11) and the factory Carrier UV bulb in the A-frame. The UV bulb is a must to keep down the mold and sterilize basically any germs, spores and viruses that pass through the system rather than acting as a breeding ground. I replace the filter twice a year and the bulb every 12-15 months. The bulb runs 24x7x365.

It might help a little. That stuff is usually algae; unless your pan is made out of metal and it is corrosion? Most pans are plastic now for that reason, the plastic basically lasts forever. Either way, cleaning the pan and adding algae killer tablets or vinegar or even bleach keeps things running. Make sure you have a float switch in case things get out of hand it won't flood your house. On my old house I used to have to run vinegar through and if things got bad, I hooked up the shop vac to the drain pipe outside.

My new house I have annual maintenance on the unit and that included keeping the lines sucked out and adding algae killer. For $75 a year the onsite annual checkup and maintenance is a no brainer.

Yep the light would definitely damage the filter over time. The light has a metal shield below it to prevent damage.