I am super attracted to the idea because I love to fix and flip, and the emount of money to get started is so much less. 

That seems to be the main reason he left.

The full payment would be around $5,400 : The ADU could rent for $2k per month and you would be left with $3,400 per month on the main home.

From a property appreciation / ROI-on-sale point of view, its unclear how attractive such a property would be for a future buyer.Would really appreciate your thoughts on this Invest 5S proposition or similar build-to-rent units.

My main concern would be the occurrence of an emergency before I had time to build up a sufficient reserve fund.

I'm based in the Seattle area, but my main real estate focus is in midwest market (Memphis and Detroit) To be clear, I wasn't making as much as you but I was able to put myself in position to leave my W2 . . . for now.

If you are not in a good neighborhood, you will not be attracting great tenants and sharing a duplex with someone can be a highly stressful and unpleasant experience, especially if the structure is not truly conducive to being a duplex.

Now mainly because of this boat, he is Not paying rent for this month and wants to leave(I'm happy that he wants to go).

There is a good real estate professional group in the area that I think mainly communicate via Facebook.

@Kasondra Milton- hi there ...thanks ...Raised in the fairport area ...live on west coast now ..last summer I had to return to Roch area to help with a family illness  situation ...I stayed in a AIRBNB that was close to Strong hospital for 3 weeks ...in my search for places - I must say I was surprised at the lack of options ( at least at that time ) ...that being said - I agree with your comment about the fact that Greater  Roch  likely  wont  attract a large amount of renters consitently  ( outskirts  like  finger lakes are a diff story ) - thanks and good luck