Basically I have a builder who is looking at land to build on and is giving us the opportunity to bring an investor to the table.

If the Real estate agent brought the deal to the table.Then they are a greater partner.Who ever brought the deal to the table should be in control.A lot of a partnership arrangement is who is funding the deal is the most valuable unless the work is funding by another partner and/or that partner puts in more than the funding.From your post, if they don't agree to pay your worth, get different partnersand put in writing everyone's split to the dollar!

I agree with the supposition that 100% occupancy reflects leaving some money on the table.

The last thing you want is for this thing to land on a lawyer's table.

We started out too low and were leaving thousands of dollars on the table.

I’m going to put together an amortization table to get a better picture!

Whatever deal they had is not legal and I don't know what the section 8 will do to you if you continue accepting cash under table, also irs may not like it.It is so hard to get a voucher for section 8, so I don't think the renter will give you hard time especially knowing she might loose her voucher for paying cash the previous landlord or to you.

.), what if any income it's generating, and what skills you bring to the table, since that'll also dictate what/if any kind of loan you can get.

Finding a deal below market and acting as a wholesaler could be the value you bring to the table. 

If you don't have a quote from a lender, as a back of the napkin way of estimating how much cash you will need to bring to the table, I suggest using 30%.