It needs new flooring throughout (about 1600 sq ft), paint, some windows need replacement, A/C units are 10+ years (there are 2).

It usually means they replaced some carpet, slapped some paint on with a cover up job, and maybe replaced some light fixtures or knobs. 

I closed on my home, did most of the remodeling myself (took the "how to tile yourself" class at Home Depot, painted, etc) and lived there for 3 years until I was able to buy the next one. 

Labor for removing old/installing new sink, cleaning, painting, etc?  

If you buy post-1978 you likely miss all of those lead-based paint, galvanized plumbing, knob-and-tube wiring, asbestos, etc. issues.

All units will need updated kitchen (plus appliances), bathroom (plus new tub, vanity, toilet), expansion of kitchen in one unit, whole new kitchen area for another unit, new floors, paint in all units, plus new HVAC, plumbing, roof...

New bath tub/tileNew FlooringNew Paint/TrimNew Vanity/FixturesNew Sink/Toliet

Paint, carpet/flooring and lights.  

We've done some small value adds - painting, new appliances, new counters, along the way.

Usually there are minor repairs, new locks, painting, repairs on the floors etc, and then we usually have a realtor who finds us a tenant property.I wouldn't let a tenant out of that responsibility.