I can assist with the real estate side of things - and probably the mortgage side too.

My endgame is to end up with $300k/yr in post-mortgage income in 20 years based on investments I make now followed by continued investments over the next 10-15 years own.

@Zach Howard there is no agreed upon Classification in the 1-4 unit market.We've done our best to logically create a system for our market, mostly based upon relative sale prices, but also using crime rates, rents, occupant income and a few other variables. 

Luckily the family in my rental is paying $9000/mo (3x my mortgage) so I am gaining signifigant wiggle room for mistakes.

For the 10 year period spanning December 2014-2024, single-family prices in Austin nearly doubled, yielding an annualized appreciation rate of ~9.4% in that period.

I've also held of holding properties in individual LLCs that are owned by one S corporation, which allows for a 60 / 40 split between ordinary income (regular tax) and dividends (capital gains tax rate).With the goal of minimizing taxation and liability protection, what would be the recommendation from more experienced people here?

When you sign almost all mortgage closing packages, you are signing an Occupancy Clause that states you are intending to live in the home for 12 months.  

We helped her move to PA from FL, provided a furnished apartment at a reduced rate for a while, etc.

Some areas still offer strong appreciation potential along with steady cash flow, and when working with trusted lenders, you can find competitive rates in places like Memphis, Little Rock, and Oklahoma City, which tend to perform well on both fronts.

Many likely have coverage for their mortgage balance or from many years ago.