So if your using margin at let's say 12% interest rate, to do the mentioned S&P gaining at 8% or heck let's say 10%.... congratulations you just found a neat way to go a couple hundred thousand into debt.

Homeowners who sell their primary residence must pay taxes on profits exceeding $250,000 (or $500,000 for married couples).

Between now and the time you retire, there will be a couple of severe recessions and likely serious inflation. 

I have two banks that have done so as well as a credit card, and know of a couple of organizations that have as well.

If you need an LLC for tax reasons later, you can move title into an LLC later for a couple hundred bucks.

Honestly if you are doing STR I would suggest doing Austin itself rather than all the way out there in Kyle - maybe a couple of years ago when the prices were through the roof in Austin city itself this would be a good alternative but there is a blip right now where you can get a god entry point in Austin (downtown/east ideally) for STR

A couple problems dividing a property and selling in a “Timely” manner and then picking exchange properties of equal or greater value than the lots you sale.  

That is a safe harbor from the IRS with a couple of caveats. 

Indisposed the next couple days but will reach out soon!

Whats making you think rates wont go down after a couple years given the new administration in charge?