No formula can be accurate across the board because even “cookie cutter” properties next store to each other differ as to view, location to the street, topography of the land, lot size, physical condition of the property, past remodeling, quality of the mechanical systems, sunlight, utility bills, past use, etc.  

Furnished mid and short term rentals will cash flow if managed correctly and you find the right location and property size. 

What are the lot sizes?

Unless the place in an amazing location that couldn't support a full size home, you are better off doing a regular place.A tiny home isn't considered real property.

Depending on loan size and what the DSCR ratio is, I have a lender that would be 6.88 to 6.99% with no points with a 680+ credit score and 20% down. 

Worked out well for us but by saving the sellers agent fee he no doubt left money on the table.  

It's not that big of a problem if the zoning allows for 3 units on a property of that size, however in most cases like this the conversion would have been done illegally or at the very least is no longer a conforming use.The shared water meter is pretty typical for multifamily here in Tampa.

Water table is high due to these rain water drainage issues.

Provide four to five copies of drawings size 24"x 36" and 11 each Site Plan/ Boundary Survey.

Ignoring short-term bridge loans, most commercial loan sizing is limited by DSCR, but they are not called DSCR loans.