I just dealt with some too, found a poorly installed window that was letting water pour into the block walls (basement unit) every time it rained.  

The are super simple self install items that you can put in your house when its vacant and when you rent the house you put the alarm components back in the box, put it back on your closet shelf, go onto your phone app and stop the monitoring service until the house is empty and your portable security system is back in place. 

So we moved in a new previously bought scratch & dent LG (dent in left side didn't show once installed).

When I purchased the unit, I had the room completely gutted and a new bathroom installed.

Just like you don't spend money learning how to install an HVAC system to a house because the one you bought needs a new one, use a financial consultant if you do not have the experience. 

@Jaron Smith usually the crawlspace is a ventilated area, so unless you plan to dehumidify the neighborhood I would'nt waste the effort and money to install anything in there.

Does anyone know of a reliable HVAC person that has access to used or new units that can do this install asap.

If you don't have exhaust fans in bathrooms, install those as well as one in the kitchen above the stove. 

Once you start getting in the $4+/sf range of this stuff you start getting some real tough, virtually indistinguishable product that has the added benefit of easier installation and being waterproof.

Finished the upstairs, including the 2 bedrooms and bathroom and finished installation of the upstairs HVAC.