The 2 smaller units both received a face lift with a fresh coat of paint, new hardware, and new counter tops and both rent for $900/each.After all the renovations, the estimated ARV is currently sitting at $550k-$570k. 

I have two options: 1) I can leave the paneling and apply a fresh coat of paint over it or 2) Remove all the wood paneling and replace it with sheetrock and paint.

Consider getting any metal coated (exchanger for heat pump etc).

He bought them white vinyl, had them installed, sanded down the frames, slapped on a coat of bonding primer, then exterior colormatched paint. 

If you decide to resell it, I think a simple cleanout, MAYBE flooring, and a full coat of paint will get you the best ROI in this market. 4.

BUT he did 4 coats of poly not 2 - as he said to make it indestructible.

Once we patched up the drywall, added new carpet, and a fresh coat of paint, the house showed very well.

You have two choices, demo the entire lid and add new drywall or get a good drywall crew to skim coat the entire ceiling.

Getting a good smooth wall without putting multiple coats of mud on takes time to develop the skill.

In the south the coating is on the outside to block the heat from the outside.