Our long term goal is to purchase and move to a remote ranch and for me to be able to quit my job around 40 years old.

I realize these are already very good terms, but I thought I'd check what is possible.

Say a "partner" comes in and it's say the unit is set, rent stabilized with a 3yr term. 

Long term $ can range from 6's-10% range depending on all types of factors - LTV, location, unit count, debt coverage, borrower strength, full doc or lite doc programs, etc..

Working with the city to find a solution.There is a similar situation near me where an investor bought a short term rental house, rehabbed it, ran it for a while, and then got in trouble with the town after a neighbor complained and the town said short term rentals weren't allowed in the community. 

I've never seen a new STR law that didn't grandfather in existing permitted short-term rentals.

a lot of people will poo poo this, but I also live in a market where cash flow is low, property taxes are high and properties are expensive (which is a relative term).

Any tips you could give me on this in terms of viability?

Leverage magnifies return. 3) The effort involved in adding an ADU is comparable or larger than a rehab associated with a BRRRR.

The reason I ask is because most deals I see on Crexi or Loopnet or anywhere else create negative cash flow under 7 or even 10 year terms with 7% - 8% interest rate.