This year I didn't play musical chairs because my regular interest rates were so low it wasn't worth the hassle.

I understand your point but in my opinion you can say the same for a person with a regular job without other source of income.

We are in a small town and have a famous flea market so it rents regularly every month, but not all the time. 

expenses fall into one of two buckets.Expenses that need to be pro-rated - These are expenses that is one amount and benefits both the main home and the ADUExpenses that are only applicable to the ADU - These are items such as repairs/supplies to the ADU.

Just regular keys and are copiable.

He supplied me with a “blank” contract that he uses for the situation (different for residential and commercial of course).  

Limited supply, large population centers, tend to be strong markets.

-If the sale involves a note, regular and timely payments on the note should be made, and repayment should be based on the value of the underlying property rather than the success of the land development.

We chose it because I grew up there, but it has been a good investment for us.Now we could have made more ROI in a different area, but we wanted to use it regularly. 

We have a very low supply (1.5 million houses short) materials are out of this world so that will push the cost to build up more and there is a massive labor shortage.