Realtors want clients who will work with them through thick and thin.

If you keep the popcorn ceiling, a coat of ceiling paint will do wonders to lighten it up.Position the ceiling fan so it is over a table and you won't have to worry about banging your head.You're right, the actual ceiling height wouldn't change by more than the thickness of the drywall, but it feels more tall and open with the space between the rafters. 

If it was my project, I would try to focus on getting people into a few finished units ASAP just to cut down the bleeding of 16 empty units.The 1/3" plywood is probably a good suggestion and is probably the correct way to solve the problem.Fixall and a belt sander will probably also do the trick to solve the problem for a little cheaper but a bit more labor.Alternatively, some carpet with thick pad for now could also be a reasonable solution.

The guy had a very thick Indian accent.

The floor is 8'' thick precast concrete slabs so support isn't the concern. but i think that the direction I'm m leaning towards. fix the foundation and be done with it.

Wet mil thickness plays a key role in paint usage.

He used to sell door to door years ago and talks about the thick skin he gained from the rejection he dealt with.

I think there are also extra thick/heavy paint products which could be sprayed over the popcorn to help seal and stabilize it.   

He helped me through the thick of it.

I used the wrong joint compound (non thick structural stuff) and we're seeing some cracking here and there.