I am a lawyer and this looks like you are admitting to breaking the law.

But what you’re encouraging is that when I am 23, I should use the first 4 or so years just building a portfolio of LTR’s and then when I am 27, look into leveraging STR’s to meet the “Real Estate Professional Status” and “Material Participation” the IRS outlines, correct? 

Sorry, i have been doing this for about 5 years, but never ran into someone bringing in their adult kids in after leasing.Maybe that's it. 

Things will inevitably break, jam, clog, drain, build up, wear down, etc. over the course of a year.

Given how many gurus are marketing and pushing consumers to get into Airbnb arbitrage it has created a massive amount of saturation across many markets.

Just like any strategy it depends on your goals and how a MTR fits into those and your other investments. 

Transitioning into hard money lending is a natural step given your experience.

Or getting into commercial? 

For newly constructed, purchased or renovated properties and also retroactive generally over the last 10 years, building components are properly classified into individual units of property and accurate recovery periods for computing depreciation deductions.

I don't see many with any amenities at all and building them into a budget with only 4 units usually isn't feasible.