I would upgrade properties every 12-15 months as allowed by low down payment loans if my significant other wasn’t risk adverse and opposed to moving.

And if it were set up where everything went through a title company so the buyer pays the title company, they manage the buyer's loan (from me), and the title company ensures my mortgage is paid without my direct involvement... what parts of the transaction would feel risky or not worth the headache to you? 

Other than paying for an appraisal or BPO (and maybe a credit report), you should not pay a lender anything until your loan funds.

@Patrick Roberts & @Tim Delaney- which lenders/ loan types are good for 80%?

The two existing LTR units (on my family’s property) were built 5–8 years ago at a cost of about $80,000 per unit, so I’m estimating a 20% increase in costs for the new builds.My plan is to use the equity in the land as the down payment for the construction loan, which I expect will make closing costs the primary upfront expense.

10% down 2nd home loan and savings from the proceeds of already owned STR's.

These names frequently come up in investor circles because of their reliability.Speak Directly to Their Team: Legitimate lenders will have knowledgeable representatives willing to explain their loan products and processes in detail.

If so what are his loan requirements?

Most 1-4 unit real estate investors are using DSCR loans right now for any buy and holds while flippers lean on higher leverage bridge/fix and flip loan options with higher interest rates.

Often, lenders will not act until the differential between current interest rates and the interest rate on the subject loan reaches a certain point.