Are you adding window units or central air?

However as @Jordan Moorhead mentioned, small multifamily (1 - 4 units) typically yields higher rent to purchase price ratios.  

I'm prior Air Force and I agree with the above comments that first and foremost you should work on your real estate education and make sure you want to be a landlord.  

So it turns out they recommended replacing this part called a capacitor that from my understanding, initiates the startup of the blower within the AC and allows the air to start flowing.

Central Heat/Air.

You guys might like the story of a literal "Air" BnB where private pilots land and park their planes and stay at my cabin and use the place as staging ground for low level recreational flights across national parks.

After the possum has been removed from your home, then you may want to call a professional heating and air conditioning company to come and take a look at your ductwork.

Would you leave the air conditioning on when they are gone, or would you turn it off and turn it back on the day they are supposed to arrive? 

If you can easily disconnect the drain pipe at the furnace, and you have access to an air compressor: disconnect the drain pipe, have an accomplice plug a blow gun into the air compressor, and then blow air into the pipe - the same direction the water flows now. 

It's all still up in the air.