I'm thinking old houses needs major repairs such as air conditioning/ducts/plumbing/hazard material removal (popcorn ceiling, asbestos, lead) if not done yet.  

I have only one rental property but it cost me $1,000 to have the living room and kitchen painted, have some parts of ceiling repaired, and part of basement wall plastered.

Find some nice ones and put some molding at the top of them to the ceiling and they will pass as custom.  

Walls, trim, doors, ceilings. 

We leverage contractors as well but I'll happily paint a few ceiling and bedrooms to save thousands of dollars. 

Typically the ARM products have a Ceiling which can be 5-6% added to the rate. 

Painted inside, fixed up the bathroom in the second unit, put up new lighting and added ceiling fans/lights.

, fixtures (ceiling fans), patio vs deck?

- Redo electrical wiring and lights- Redo all drywall - New floors - New insulation - New ceiling deck

So you will probably have to cut out a section of ceiling in the unit below to repair the ceiling anyway; you might want to consider doing that now to examine the nature of the water problem better.