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%.

Doing it Leon Johnson style with "Now I'm going to get real personal now, if I brought that $650k in cash in a brown paper bag, and set it on the table, what would you do with the money?"

However our credit is poor, and I have been working under the table for quite some time, therefore have no proof of income.

However our credit is poor, and I have been working under the table for quite some time, therefore have no proof of income.

However our credit is poor, and I have been working under the table for quite some time, therefore have no proof of income.

If you are just putting it up on AIR/VRBO and hoping that someone chooses your unit, you are leaving money on the table, IMO.