I was thinking that I could put up the money on the home and just collect a "mortgage" payment from him.This seems very risky to me because he essentially has no skin in the game, besides having a place that he and his family can live for $350 per month. 

Even at a low purchase price of $50-75k in Detroit for an 8 unit (which is very possible but not be in a good area where you can charge market rent), a basic rehab budget of $5-$15K per unit puts you at an additional $40k-120k in repairs, which is essentially all of your $150k. 

Yes essentially that is it.

So essentially they average up their return from 0%, to 6%, 12%, etc as they buy more liens.I also went to my first tax lien auction a few weeks ago and competed with people bidding three times the tax lien value for premium.

The two party "swap" is the easiest because two parties essentially swap properties with each other. 

Note; on this deal I have partnered 50/50 with a contractor; he is not being paid for the work; essentially he is renovating for free in exchange for 50% profit, so my labor costs are very low (bringing in subs for some small items and day labor to help, but no large labor costs).

that's essentially buying a job... by quitting one.

Knowing how to ensure the closing goes smoothly and quickly the FIRST time is essential.

Can you add additional landscape elements to compliment your choice color?

That is  even more concerning, since I would essentially be relying on him to pay the rent.