To make sales and penetrate that market will be very tough to do.

a semi gloss or gloss paint will probably do better in a humid bathroom so that the moisture drips off the walls instead of soaking in.

The seller seems to think they can sell it for what their father bought it for 10 years ago, but it is very outdated and currently has ventilation issues in the upstairs living quarters, there is a lot of moisture on the walls.

The reasoning is that you've created a 2nd vapor barrier that creates moisture that has nowhere to go other than into the roof panels and as a consequence gives you rot which will have to be dealt with 10-15 years down the road.

Property Managers only have about a 30% market penetration into the overall rental market both in San Antonio and Nationwide.  

You need to find the source of the mold: leaking water pipe/roof, ground water penetration, drain pipe leak, windows/siding aren't weather tight or flashed correctly and they let rain in, gutters and downspouts aren't working correctly, or tenants are screwing with you intentionally.

Tenant agrees to allow Landlord timely access to premises to do maintenance and repair.Tenant will notify Landlord in a timely manner of any damages or problems as they arise, including damages caused by Tenant, malfunction of appliances or fixtures, and water/moisture leaks and spots.Tenant will take care of the premises, keeping them clean and clear of debris.

If you penetrate the roof for new plumbing vent, install new gutters or any other roof work this can cause a inspector to write it up, and insurance inspections can be deny because of it.

I have my home inspection and termite/moisture inspection tomorrow afternoon and will be getting the official mortgage documents in order as soon as the inspections both satisfy me.I will be getting a conventional bank mortgage at 5.25% with 20% down and 2 points.

Mold will not grow if you have the moisture in control, it needs moisture to continue to live.