To be upfront, it's very difficult/nearly impossible to jump into real estate full-time.

Austin has rather strict zoning laws and changing those can be arduous and most likely impossible except in rare situations.  

It is also going to be near impossible to find a company that will fund a 10% down mortgage.

Without knowing the details of the deal, it's impossible to know.

It makes something like getting loan for 200k and seller financing 100k impossible, as I understand it, because he is basically in a 1st lien position?

You won't make much money upfront but over several decades that won't make much difference.However, if you want to buy or sell in the wholesale market (for cash or terms) working with realtors is nearly impossible.

Prices are still high, and back end buyers are unmotivated, so its getting squeezed on both ends, unless you find a home run deal which is nearly impossible for new investors.

The downside to these regulations is that it has become difficult (but not impossible) to find properties that can be legally used as STRs in the area.

It is near impossible to assess whether this is a good deal or a bad deal based on what is here. 

Without knowing where you are going over, it's impossible to tell you what is appropriate or not.