I'm sure that there are other measures as well that can be taken if they do not get removed by the simple challenge, but that's a place to start.

This could be also measured in total profits including ROE vs cash flow alone.

What other measures would/do you use to calculate ROI on this type of property?

I've been reading "The changing world order" by Ray Dalio, and listening to some podcasts related to the subject of the declining US empire, and I'll admit it has me wondering if everything we hold true about long-term investing may be in for a shakeup in the near futureWhat I'm trying to decide is, should I sell a rental duplex (I have 2) and pay off my primary as a defensive measure?

But you need to be even keeled and scrutinies of where you put your money, so measure a hundred times and cut once.

Additionally, government stimulus measures have led to inflation, driving up the prices of everything, including real estate.Why aren't prices coming down?

I think your goals are very realistic and measurable.

Is there some type of measurements as a guideline to specify what is consider within the “Geograpgic Area”?

The 2 garage  measures 17'x20'.

Slow, steady, measured growth to that level is doable and I wish you all the best.