Wallpaper, Pepto Bismol bath tile totally gets me excited.  

We are planning construction of two 24-story towers with a total construction floor area of 70,000 square feet over a two year period.  

The total of these land contracts/mortgages is about $780k. 

(I would have to provide $120,000 for 20% down payment, leaving a total loan amount of $480,000)...The $480,000 goes to the seller (more than half of the asking price which is more than what he requires for owner financing)...The seller then credits back to me $120,000 at closing, creating an owner financed loan of $240,000 and giving me a no money down deal.

The upleg for this 1031 will be roughly a 60M total equity position with about the same amount of debt; i.e. a total cap of $120m and will be using all of the proceeds. 

Maintain a decent cash reserves to cover vacancies, maintenance, CapEx, and mortgage payments encase of total income loss.  

If I buy 10 mobile homes in Mobile Home Parks and buy & rehab for a total of $5k and the turn around and sell them for $20k and finance for 60 months in a 2018, what is the profit I pay taxes on in 2018?

If I buy 10 mobile homes (no land) in Mobile Home rented Parks & rehab for a total of $5k.

If it is not possible I was thinking of doing a “cost share” billing plan, basically dividing the total bill for SWT by 4 units.

If they did not break out labor and materials - then your only option is to issue a 1099 for the total amount.