I am in the begining stages of producing a conce0t drawing for the rental property.

Hello Allen,Last year, we conducted a study with a few clients and produced a white paper.

Real estate investments (STRs, MTRs, live in flips) have produced my best returns by a good margin.

Same logic applies here as it does to your previous experience, there's just simply an added layer of the income produced by the property. 

in a few short years 1 property has produced over a $1/2 million in equity, thousands in cash flow, was leverage to buy another property which does the same and leverage to buy a small cash flowing business. 

The hedge funds and firms alone are buying more supply than is being produced. 

When the money dries up, they'll leave just as quickly as they arrived and you may be stuck with a real mess.If it can produce more money as a short-term rental, do it yourself.

I self-manage and produce $700 in pure cash flow each month.Lessons learned?

Consider selling the duplex to put it into a higher income producing asset (out of state, DST, something).

This amounts to lost opportunity because if you had purchased RE, at the closing it can start producing return. 5) ADUs detract from the existing structure whether this is privacy, a garage, or just yard space. 6) this is related to number 1, but there are many more buyers looking to purchase homes for their family than there are RE investors looking to purchase small unit count properties.