My home is only 1/2 mile from the water, thus it is spared the driving salt and rains, excessive moisture, and sand damage from homes directly on the water.

It could go tomorrow or it may last another 10 years4) Any idea what's causing the mold- what's the moisture source?

As far as leaks, a moisture meter will tell you if it’s an active leak.

Below are the details, please let me know if there are any bases left to be covered, additional questions I should have answered, etc: - 3 Bed, 1 Bath, 1106 SF- $695/month, current rent value is $1000-$1100/mo - Tenant pays on time - There's a mild subfloor/foundation issue in the corner of a room (realtors guess is that it could be a failed rim joist from moisture - is this an expensive fix?) 

There was no fan in the bathroom to remove the moisture.

Below are the details, please let me know if there are any bases left to be covered, additional questions I should have answered, etc: - 3 Bed, 1 Bath, 1106 SF- $695/month, current rent value is $1000-$1100/mo - Tenant pays on time - There's a mild subfloor/foundation issue in the corner of a room (realtors guess is that it could be a failed rim joist from moisture - is this an expensive fix?) 

I would be gentle at first and remind him how long it has taken and Your willing to be easier to communicate with and make quicker decisions!

Based on what you've described, this sounds like moisture on the surface of the wall, which would be caused by excess moisture in those areas from the Tenant not ventilating the bathroom while showering or cooking with a lot of steam in the kitchen area.A contractor can put a moisture meter in the sheet rock and quickly tell if there is any moisture inside.

Moisture/water intrusion along rear wall of home during heavy rains (there is some negative sloping at the back of the house).2.

I can control the temperature of the house, the locks on the doors, cameras to see what's going on outside, sensors for moisture/freezing in the basement, door sensors for doors that shouldn't be open and a lot more.