If you have a mortgage, it'll get a bit tricky to enter the data (principal, interest, and escrow.)

You are arguing basic economic reality backed by quantitative data, as well as overwhelming anecdotal evidence.

On the surface it also sounds like you have a lot of local support for managing and maintaining the property but I suspect that will kill off most of the returns.The real information is somewhat hard to come by as the developer controls much of the market, the rental management, and a lot of the previous pricing data as they didn't report to MLS for much of their history.  

We agents enter the data into the platform, it doesn't get there magically.

It doesn't matter if you're using it as an MTR - you can just input all those data points.

I just looked at the data on airdna as suggested to see the estimated income for STR.

If the 4-plex is properly analyzed, and the data suggests $800/month cash flow after vacancy, Capex, and repair budgeting, then it sounds like a solid deal.

The reason they can give free skip trace data is because it's such dated and poor quality they are getting it at little to no cost.  

Consult Historical Zoning Information: Combine what you see on Google Maps with historical zoning data available from local city planning offices.

Should I wait and build once we have more data about the future economy or take the plunge?