No (institutional) lender will finance 100% of your purchase price as a purchase, all lenders want "skin in the game".

I'll check around with some lenders to see what they share about their comfort with the timeline - whether HELOC or not.  

Using local hard money lenders usually works best.

just double checked my lender is now 80% LTV for short term rentals only 85% for long term rentals

By reducing the principal balance, your lender recalculates your monthly payment based on the new, lower balance.How Does Mortgage Recasting Work?

I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

Taa da da - what happens if the original lender enforces the Due On Sale?

What would be my best approach, I assume find a private lender and work out some deal with them.All questions and answers will help thank you.Normally the lender for the reverse mortgage will start a foreclosure.

Their might be some wiggle room if what is being collected comes in over the market rent however for the most part the market rent would be the preferred guideline and any deviation from that would be up to the lender that you are working with.

The companies you will find in the lender finder section of BP are probably mostly companies as opposed to a private person like you are referring to.