I have a W-2 job primary and my business partner has another business.

Get a job in property management.

Good job on this flip!  

ADU zone expansion is not certain, and even then who knows what the rules will be (owner-occupied requirement, etc).

In this case, correct, 1031 exchange is not available. 1031 exchange is property for property, and an interest in a partnership normally is not (with a few rare exceptions, so you may want someone knowledgeable to give you a second opinion for your particular situation, which requires reading your inheritance documents.)Whether or not you have any mitigation strategies totally depends on your specific situation and requires a one-on-one. 

Also since it's a 4-unit it would need to meet the sustainability requirement. 

First, is it required by law for a buyer to sign a buyer's agreement before they start touring homes?

I suspect if someone contests could be longer.I also think once you go to mediation this will get worked out pretty quick mediators if you get a good one do a nice job putting these deals together..

There’s a ton of investment pouring in, job growth, and a growing demand for housing.

Quote from @Pamela Rivas: Hi Natasha,Here are some key points to consider about setting up a Mexican corporation:Setup Costs: $1,500–$3,000 USDOngoing Costs: $1,000–$2,000 USD/year (accounting and tax filings)Benefits: Tax deductions for expenses like maintenance, repairs, and managementBest for: Multiple properties or income-generating investmentsWhile a corporation is ideal for managing multiple properties, it’s NOT required to obtain an RFC.