Wow, that seems way high to me. 117 houses puts you in pretty rarified air as far as RE investors goes.

Air b&b?  

Air BNB is fine if the property is on your schedule E and you are claiming your income. 

The AC/central air does not work.

Airforce base short term rentals, I saw a lot of air bnbs around airforce base for graduation.

When we pull permit for the additional bathroom, inspector delay signing due to some minor things like incorrect pipe material for the bathroom, electrical sub-panel is not up to date, central air heat certification needed, etc...

Thing is, this house was poorly remediated, they didn't cut high enough or even let all the furniture, belongs, etc. to air out.

Does anyone have any experience with  this type of forced air furnace? 

The first floor has central air and forced air heat, while the second floor has steam radiators and no AC.My wife and I plan to live here for many years, and would like to either (1) duplex the first floor unit down into the basement and keep the top floor as a rental unit; or (2) duplex the first floor up into the second floor unit and convert the basement into a rental unit (we believe it could be a 2-3BR, 1.5-2BA unit).  

After you address the leak it might be worth looking at additional venting or conditioning the crawlspace with a duct from the air system.