Would a bank even allow us to mortgage multiple buildings on a single lot without it being subdivided?

Study what kind of properties sell, for how much, and what kind of tenants live there.Think with a 10year+ vision, but a decently sound property (not a 1900 single family conversion that is begging for a full gut rehab), and but in the RIGHT location. 

., "I will buy at least one single-family home, duplex, triplex, or fourplex before the end of 2019") and then do it.

I've done several of these here in Chicago, and currently looking for a single-family house to a live in flip in. 

You can get solid cash-flowing single families in the 90-120k price range and duplexes in the 130-180k price range.

When I worked with a property management company, we had someone buy a unit (single family) that had a STR and marketed it as a STR.

I have three single family rentals for three years and I now have my first horror story.

If you know anything about duplex builders (most seem to be single family only?)

You could do General Contracting where you'd need knowledge of all trades or manage a team of one single trade. 

It's a pleasure to meet you, Andy.. are you considering venturing beyond single-family homes down the line?