If you are looking for great areas to cashflow and very reasonable ARV's that allow for value add investment strategies, I can't reccomend whitehall enough.

The first thing to ask is your exit strategy on the second property - are you simply buying a rental or doing value-add?

I have seen more people torch their retirement plan using this "strategy" than I care to think about.As @Chris Seveney notes, an IRA can be setup with a specialty self-directed custodian so the IRA can be invested in non-traditional assets like real estate. 

Are there specific strategies or platforms for connecting with potential development partners open to joint ventures or revenue-sharing models?

It's not just data; it's knowledge, empowerment and opportunity rolled into one groundbreaking solution.However SMFLs aspirations go beyond this.

Are there any data sources that can help me select which areas of San Antonio are growing and would be good investment areas?

With that strategy you're keeping more in reserve and earning interest and possibly seeing appreciation.

If you need MLS data, partner with a Realtor who can send you a list of all the items in a Zip Code.

I would be interested to see the PriceLabs market data on the 3 markets you've mentioned, and how they compare to Gatlinburg, TN or Joshua Tree, CA.  

I have not purchased the program so I cannot comment on it, but as a note investor it depends on what your strategy is.