Your best bet is to either get a job working for a PM or partner with a PM to build the business.

My question is, since there is flexibility with the building itself, what would be best loan option to go with that would work for this property in terms of best rates, lowest down payment? 

I think you need to more likely look at a CTP (construction to permanent) loan and your best bet with that tends to be a local banker in your area.  

Land contracts often allow for a higher price, typically 5% - 10% above market value, due to the flexibility they offer buyers.What's the average interest rates charged on these relative to regular mortgage rates?

To be clear, the lender is in the family and he is pretty flexible if I can say.

I’d bet over 99% of people who learn about it in his system fail at it and It costs $1000 or more to get started.

In this way the ADU does not need to be in a corner and the layout is a lot more flexible.  

Hi James, Your best bet is to search Google or BiggerPockets for hard money lenders in your area.However, you can also contact private money lenders directly and shop around for the best price yourself. 

Quote from @Chris Seveney: @Brian CarberryI wish Vegas would carry betting lines for candidate agendas.

Or is Indio a good safe bet with potential appreciation - especially the Terra Lago area?