It is likely that even the initial transaction may be a disqualified party transaction if you have existing joint ventures with this individual.  

Build the system, step away, be a service missionary with my wife and kids (e.g. bring clean water systems to third-world villages, disaster relief, etc.)"

The caregiver was not family and the old man did not want to disinherit his biological heirs  so he provided the home at a modest price but he made the estate the beneficiary of a modest  private money mortgage to provide a monthly remainder for his own adult children who already owned other residences in the same community.All parties were served by this arrangement until the nurse's own son developed leukemia brought exorbitant demands for both money and time causing.  

As long as there is nothing prohibiting it in your state statues, any agreement between to parties is enforceable.

The most important part is the cost and the potential rental and whether it's partly for your own use?  

Full transparency for both parties.  

I'm also looking at an auction.com property which is up for its third listing on auction.com.  

The third move would be to find an affordable flip and jump in to real estate investment aiming you enjoy it. 

They may agree to drop 5% or so off the sales price if you were paying cash or had 3rd party funding since they would be receiving their large lump sum in one shot.

Subordination agreements would be recorded (and they aren't all that common), so just be sure to watch out for them.If there are three loans recorded, and no subordination agreements, and you buy at a foreclosure sale of the middle one, you are buying it subject to the first one but the third one is wiped out.