You can get regular residential financing (backed by freddie/fannie) for up to 4 units.

If you are serious about wholesaling I can give some unvetted advice as i'm just breaking in myself but am having regular conversations with sellers.

I would do a regular lease with a 3 month term and require the entire 3 months be paid in advance.

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.