With your hypothetical question -its loaded questions and you will get 100 answers- I have SFR that performs better than these numbers. 

========Regarding adding a unit, some things that come to my mind are (not an exhaustive list):Making sure the Zoning will handle the extra unit, and you have some plan for parking the extra vehicle(s), and that the sewer and water service can handle the extra load, as well as the electrical service drop has enough extra amperage available to satisfy the electrical code requirements of another unit.You may also want to look into if there are extra fire requirements for three units, such as having to add a fire escape, or fire extinguishers, or interior sprinklers.And sometimes major electrical work will require the whole building be brought up to current electrical code.A local architect with local building upgrades like this in his portfolio might be a good addition to your Swiss Army Knife. 

I don't want large pets so I plan to restrict the weight to 20lbs.

If I unplug the pool pump and reset breaker it still trips under zero load. 

He charges a fee to mediate the process, and from what I have heard / read is worth his weight.

But as a few above have stated, there is often a heavy fee-load with these products. 

You’ll need to spend everything you got for the investment property and have the same debt load (minus some closing costs).  

Now that the world has had more experience and acceptance of working remotely, I think these Virtual Tours will carry a lot more weight than they once did. 

Probably would be fine until winter.. but a MI snowfall on it I've got to imagine it would fall with that kind of weight on it. 

You could do light weight foam-crete as well for prefab walls.