Save your money and build a  network of realtors , real estate investors and  go to meetups

In many parts of the country a two unit building containing an upper unit and a lower unit is referred to as a flat.

Also, is there any form of legal document that I should potentially have the tenant sign if I do decide to hold the unit for them?

However, it is hard to gauge the rental potential so many years into the future with new construction SFH and apartments being built in the next few years.I’m worried about the HOA, the rental potential, whether I should keep saving and buy a SFH, or if I should just take the plunge and start building equity.

I'm going to assume the obvious that it is tied to a home, land, commercial building, etc.?

Likely it's that they legally have to have a physical address and as they meet clients at clients home, have them pick out roofing in a catalog and have it delivered directly to the client, there's no need for a physical building.

At the top of your screen you will find a section called "Build your Team" There, you can connect with property managers, realtors, lenders, and CPAs that specialize in real estate, and you will find Cincinnati well represented with highly reviewed professionals, by members of BiggerPockets, who are eager to compete for your business. 

I have personally been raked over the coals on some south side properties with squatters because I wasn't prepared for the time it would take to stabalize the building.

I'm looking into the Credit Stacking program that Jack McColl runs. Looking for any reviews from previous students. 
It's a program that helps/teaches you how to access business credit to fund your business endeavors...

I have bought and sold six homes, had one beautiful flip, and kept one duplex that was a BRRR score and currently building two more duplexes with the opportunity for one more that is build ready.