I'm an air traffic controller which puts me in a great position to invest in real estate.

It's a Ranch style home with a partial basement, forced air heating, built in the 60's.

If it's clear I'd take steps to prevent ingress by WDO.

The problem w/ high vacancy is those who may be considering buying a condo to live may not be able to get financing because vacancy is too high.Our rule of thumb for condos- If the bldg has little to no vacancy (its thus desirable) & the HOA rules don't prevent rentals & the HOA fees support the cash flow numbers then hit the offer button.  

In the last 6 months or so: a new roof (I knew it was needed and put it off for about a year), 3 new A/C units, one water heater, and one house needing a new air handler (estimated cost $1200).

Depending on what we decide to do with the current floor plans - the kitchens are tiny (upstairs is 8x8) - we may take all external walls back to the studs and properly insulate and air-seal the envelope (likely with closed cell foam as I expect there to be limited wall cavity space).  

it doesn't say but I believe it's 5 based on the amount of air conditioners it says it has

I made a slight detour and transferred my at&t job to the Pittsburgh area where I studied Air Traffic Control at a community college.  

Attics should be vented by pulling air from the soffits and venting out near the top of the ridge.

But, we found that the companies with the best recommendations were often the worst.We just had a license HVAC place install an air conditioner.