Should we turn off the breaker for a particular light if there is water dripping from that fixture due to a A/C drain pan leak above it?

I would.

Next I would do what I could to get the spill dried up.

Then I would make sure all of the electrical connections are dry and that the insulation around the fixture is dry before resetting the breaker.

Definitely throw the breaker before trying to work on that light. The light may have the hot wire in the junction box and simply turning the switch on the wall to off may not remove the current from that lights housing. The insullation around the light should be replaced. It will take forever to dry out and may cause moisture related organisms to develop. Placing a fan in the attic next to the problem area should assist in drying out the drywall/plaster. Pour some bleach water 50-50 in the condensate line to assist in removing any algae that may have cause the clog. If that doesn't fix the clog you may need to snake it out and/or blow out the line with an air compressor.

We don't actually have a clog. The issue with the pan is that it has rusted out and must have multiple holes. We found the issue when I saw on a door jamb, below where the unit is in the attic, had drips of water running down it and the paint was peeling. So we are guessing it is down in the walls and got stopped by the header and then ran down the jamb. So we have multiple issues. That was yesterday and now, today, is when the light started dripping. Unfortunately, it is unseasonably hot (80 degrees) so the air was needed for a bit today. Otherwise, we have kept it off. Thanks to both of you for the input. Really nervous what it will cost to repair all the damage.

Sorry, I assumed that the pan had a clogged condensate line and not a hole in it. I would replace the metal pan with a plastic/pvc one if possible. The wood/plywood that is under the air handler may also need to be replaced and may be too weak to support an air handler now. The wet insullation will have to go. It takes forever and a day to dry out insullation and in the mean time mold and mildew can develop and create a whole new set of issues for you. Once you get all of the wet insullation out you should be able to put some airflow around the wet areas and solve the problem before mold and mildew have time to establish. Too bad it is hot there and not nice and cool. Hot air generally contains more moisture than cold air and things dry out more quickly in cold air with proper air flow. Hopefully the wall cavity is an interior one and doesn't have insullation in it. If it is an exterior wall with insullation I would recommend removing the wall cover and dry the wall cavity out before replacing the insullation and covering it back up. The wood framing needs to have a moisture content of less than 20% before you are in the clear, anything above that can develop rot; mold; mildew etc. If you have a dehumidifier or can borrow one that will help a lot as well! It shouldn't be too expensive to repair the damage and a lot of it you can do yourself, if your pretty handy, to reduce the hours of labor costs. Removing the insullation and drywall if necessary is labor intensive and time consuming so if you can do this you can save some money on repairs and the money you save could probably pay for new insullation and drywall materials. Hope all works out well for you and yours!

Wow, such a tremendous amount of detail and such help! Thank you so much for all this information. This is fantastic! I hope we are as handy as you are!