One-person rental units are in the highest demand, and co-living directly appeals to this market.

A contract is only as good as the person enforcing it.

Tell me - someone selling their home to your son, Subject-To - is this a person who has made good life choices? 

Personally, I wouldn't offer SubTo or a Wrap, For reasons I've written about fairly extensively. https://www.biggerpockets.com/forums/70/topics/1227199-the-m...However, I would sell on "Lease Option" and that may work for you.

I personally use 40% but I'm also in a higher rent area.

I was thinking if I can talk to my neighbor about sharing the cost (I, the landlord, personally provide labor and my neighbor provide material (e.g. fence pickets)).

I am here to create a business strategy that protects personal and business investments and mitigates risk,  procure a coach or mentor, and set up tax strategies to create long-term wealth for myself and my family. 

Whether the seller was open to a buyer commission or not, I wouldn't put an additional cost into any personal purchase.  

And what if the one person you didn't check has a criminal background, has collections, and more?

Be that person who set's up some STR's there, runs em there, and really caters it to the US "bucket list" tourist.