Maybe you can be the deal-finder/house-hacker and they can be the money/qualification side. 

I thought that maybe paying cash, I won't have to worry about mortgage and just reserve money for property tax, insurance and future home repairs. 

Typically private lenders won’t you CJ long periods of time unless it’s astronomical Interest as money is constantly devalued and $100k today vs 20 or 30 years from now will seem the money essentially worthlessOnly reason it works for banks is because the money they lend actually doesn’t really exist they make it up due to fractional reserve lending

As an example, I had a resident call me for bail money at two in the morning.

So if I sell the bare land and use the 100k as a down payment on a duplex I basically need to come up with another 100k of my own money to match the down payment if I’m going to live in one half of the duplex?

It ended up being a great deal as the sellers divorced and needed money and accepted a small portion of the loan as payment in full.

And usually because the arbitrager has spent money to furnish the property, they want to make a go of the unit.

Lastly, you can use the PREVIOUS lease [if you like it and put an addendum that the original lease stands except for 1. landlord name and place where you pay money?]

Theoretically in 3 years could I refi and pull out the money she needs and lend it to her to build the house?

I personally challenge owners to look at what the Holiday Inn in Pigeon Forge and Gatlinburg are charging and they might see how much money they are leaving on the table.