I have aligned myself with some important organizations like a third party inspection company to ensure the safety of the houses, and the Tiny Home Industry Association.

If both parties get something of value out of the deal, why is it unethical?

I get the basics of how it would work, but how can I make an idea into something that would work for both parties?

Does the seller work with a third-party mortgage loan company to establish the loan that I have with him/her?

Oakland (depending on what part) is less than 30 mins away.  

Chances are most of them will know about it.Typically deed restrictions can only be enforced by another interested party, but I'm not an Attny.

I’m reading it that the seller has a note with the party he bought it from.

Perhaps a nice 1950's built bungalow.Always hire a 3rd party property inspector to give you an unbiased feel for the home.

The plot is around 26000 sf, beachfront, great tourist locationThe build quality is high, and it survived the tsunami of 2004 intactThe place is fully staffed with a manager who's been there for 19 years, with no intention of leavingThe place is one of the few in the area that holds groups (the whole complex is rented out to groups of 12-23)It is currently earning 100k eur per annum with only 50% occupancy (the owner is older and does minimum to market - old website, airbnb, booking.com, homeaway, tripadvisor)The average occupancy of the area is 74% so there is a lot of room for revenue growthThe rates haven't been raised for 3 years and it is due for a 5% rental increaseThe reviews are stellar on all sites, with many repeat clientsThe venue is ideal for weddings, reunions, parties, bdays, etc, and the staff handle everything, including an on site chefWhen you stay there it's like having your own resort on the beach to yourselfOwner will act as consultant for up to 1 year for freeSo, he wants to sell to my husband and I, as his manager and he really like us and know we would keep the staff and concept the same.

You have clearly highlighted that you are aware of the risks that you are taking and this is more than half the battle, the easier part is to define the actions required to mitigate or manage the risks.