We now employ two part time office managers, as well as 4 property managers (including myself and husband) and keep 4 maintenance workers busy enough to only work for us (although self employed).

Any suggestions as to where to look, what to look for, which strategies to employ, etc, is greatly appreciated!

If your employer signs off, then you have no issue. 

Student loans are debatable as they can be forgiven in the event of death, disability or certain employment sectors.The opportunity cost of accelerating the cheapest debt out there (your primary mortgage) can be high.

I thought San Antonio was sustainably  growing though, so I would think that wages, employment, etc would be rising right along with property prices, so that's why I was curious to get the opinions of people who know SA.Las Vegas is booming but I wouldn't be surprised if Fitch is right about the property being overvalued there.

If you are self-employed with no full time employees your business can sponsor a Solo 401(k), which has higher contributions tools and a few other 401(k) associated plan level advantages in addition to being a very flexible investing tool. 

Some of the research I'm including in my market analysis is: 1) Rent-to-Income Ratio2) Unemployment Rates3) Population Growth4) Future employment/development trends in the area (i.e. what are the major employers?

It is a good thing that you are still employed, I think.If your are stressing the importance of long term investing  I would probably recommend the same thing because of the current economy would mostly make a Fix and Flip or a Quick Flip scenario and not get a loan to do any repairs if you feel like you would still make a profit. 

@Robert Schimming taking a loan is out of the question as I’m no longer employed with the company I built it with.

It is very close to Social Security Administration which is a large employer in the area.