Any addition in the rear of the house above that first floor would need to be in compliance of the minimum rear yard depth and maximum lot coverage. 

You can't say "Oops, looks like I put too much into it, let me get that money back and walk away".You just have to do your due diligence up front to assure (as much as you can) that you will be able to get most or all of your money back.  

I appreciate the healthy skepticism regarding the low cost of the building but rest assured, I have planned this with my architects and contractors for literally over a year now, the numbers and prices are correct.

Hypothetically, if my husband were to purchase an investment property in his name and I were to lease the property from him in my name, would I be able to list that property as a short term rental and be in compliance with the primary residence rule? 

As a full-time wholesaler, I invest significant dollars in advertising, mailing, technology, offices, compliance, etc. to get deals.  

This duplex is located out of the state I live in, so property management would have to assure that the thermostat is located and locked.All good ideas so far.

With the adjoining Building it would make 10 units so cost of ADA compliance would be very little per unit and higher rents would result with ADA compliance.

The seller assures me there are none but I'll check for myself.

Another way of phrasing your goal could be: "I want assured positive cash flow, but only by buying in neighborhoods that everyone wants to get into, where I'd be taking no risk whatsoever".Good luck with that!

They keep talking about assured 10% NET annual returns and a 125% buy-back in 10 years, with everything being contractual.