In other words, diversification on a small scale (actually, within a small market space), with a cash and effort focus on the strategies that are working today.

Stable core assets that are "investment grade" and traded by large REITs in prime locales will generally trade at much lower 6%- cap rates because the risk is lower.

In other words, the observations you've made on a small scale may not hold true on a national level (they may, but that would just be coincidence).Do you have any data to support your belief in this trend?

I have a lot of things with a far greater ROI but they are difficult to scale in a meaningful way and they are not secured like RE.

I'm ready to start leveraging to scale and was considering financing all or several of them, but have started looking into just doing a business line of credit using all my curent properties as collateral.  

Scale up same way you would buying a house.Landlords may or may not be to thrilled with your ideas of the property so navigate accordingly.

Figured investors looking into that market would want to take a look at The Ultimate Guide to Grading Birmingham, Alabama Neighborhoods to gain an understanding of the types of neighborhoods in the market out there.

I am inspired to properly read up on note investing or hard money as I think for my personal situation that would bring me greater traction as I start my investing career than those first few SFRs until I am in a position to really scale up.

If you build a bit larger product the psf cost does not scale linearly because a lot of the cost is somewhat fixed.

You will need a geologist to do a soils test, a surveyor (depending your city you might be able to do a basic topography survey with boundaries or might have to do an ALTA survey) and maybe a civil engineer to do the grading/erosion control plans.