Owner is willing to owner finance but how do we structure it being that his mortgage is for all 3.

I structured it as a refinance with Fannie Mae and so long as the appraisal came in high enough it was workable, and it did.

Pay attention to this upfront>>Will you be required to build a fire Station along with buy fire engines if you exceed X residences--required by a municipality or required to have your built structures qualify for market rate insurance polices...because if the insurance on the structures is 10 times normal the valuation of the structure might be very very low.Pay attention to this upfront>>>Can you get the skilled labor (and CONCRETE) out there in a reliable manner.

Structural repairs are not allowed, such as room additions, foundation repairs, etc.

I am in need of a structural engineer urgently to evaluate some cracks on a multifamily home in Jersey City.

or other structural warning signs like large notches cut out of floor joists to run conduit? 

However, I am curious for more details though - Which structure was torn down?

If you keep 'nickel and diming,' for lack of a better term, your contributions to the deal you might as well create a pay structure for yourselves.It looks like you are both doing "work" on the deal. 

Whatever org structure you set up during the hold period will impact the next exchange.  

Those details are all up to you and can be structured anyway you think are reasonable.