Now, I'm on day 5 of demo and dumpster #2 is filling up. 

Pad your numbers...I've done 2 properties with fire and/or smoke damage and I ended up underestimating the demo on the 1st one. 

I'd like to get to a point where I can hire these homeless men and women to help with demos on properties.

I've seen inspectors require homeowners demo/remove all interior partitions ( and a kitchen) in a basement because an illegal apartment was constructed down there.  

Also, you should understand that a house that truly has to be torn down isn't worth much more than a building lot, because the cost of demo and removal has to be taken into consideration.

Your buyer might want to look at bringing in an angel investor or a joint venture partner for opening their business to buy today.The building might have way more than expected 160,000 to fix things and do build outs.Might be easier to demo the building and scrap to the foundation and build new again.

I can contribute $5k cash, $10k credit, and sweat equity with demo and cleanup.

Some platforms allow a trial period (lead pro and realeflow do for sure; rebo does NOT, but they will schedule a personal demo for you).

Demoed one unit.

This report would tell you if the best use for financial profitability would be to keep as existing, demo and build something new, etc.Yes, I would suggest you have the sewer lines checked by a licensed plumber to make sure you have no existing issues.