I have found that all three of these have been the exact same scenario, in that the owners were all three in their late 60's-early 70's and ready to cash out and retire.

What novice is going to start fresh drafting a 2-story duplex in a coastal hurricane prone region having no prior knowledge on designing or the architecture/engineering of it?

Just read this great article detailing your question via UCLAhttps://anderson-review.ucla.edu/is-the-1-trillion-coastal-housing-market-a-future-financial-crisis/ It's not if but when at this point.

If the deep river sand you will need to invest more.  

During the past 4-5 years many of the smaller Oregon Coastal towns, cities and counties have implemented either moratoriums (pauses) on new permit issuances or a cap on the number of vacation rentals permitted in a particular area. 

Bringing in sand is not legal.

Does anybody here own a small condo that is not coastal in Myrtle beach (mine is inter coastal water front)?

Given the many benefits of buying a property with cash, my plan is to use a private loan from this company and/or from family/friends to buy the property and then refinance the property using a bank loan, thereby paying off the private lender/s and getting better terms.

However if you have an old house with multiple layers of paint peeling, then you should check it before sanding it and possibly getting lead all over. 

Understand your SREC;s and run an analysis.