The ADU cannot be superior to the primary residence.

@Kris TohovitisI wouldn't recommend using your cash to pay off the mortgage on your primary residence since you can likely get a better return on that money by investing it.What's your buying criteria for the multi-family property?

Similar to you I was doing well in real estate, had 3 cashflowing properties as well as my primary home and then thought it would be a good idea to flip some early 1900's homes.

@Robert StephensonIf you have enough equity in your primary or rental you can get a HELOC or HELOAN and use the proceeds as a down payment to buy another rental.

Like you said , anyone can check the history,  I do have cameras installed and I do check twice weekly, it's not too far from my primary home . im a first time investor, is it ok to DM the listing to see if I'm missing something?  

Best thing to do is buy it as a primary or second home and then transition out into a rental. 

I have found that I get more appreciation on the single family house because I can sell it to an investor or as a primary residence.

Now, lets talk about BRRRR and a primary.

In my area this is the primary permit that is required that is virtually never got. 

I don't know your living situation but if your paying x,xxx for rent or a mortgage and instead by living in one side and renting out the other you will be paying y,yyy instead and y is less then x that's great, especially if you can rent out your primary residence and make income there too.