A good cash buyer is a great asset and I do everything in my power to not screw them over !

True, "with great power comes great responsibility" (the Bible, not Spiderman)...but, Giving is much harder to DO than it is to TALK about.

Does this couple have a will, living will, power of attorney, trust or other "elder care" documents expressing this couple's medical directives, their wishes if one or both pass on or become "hospice bound"?

Have a real wireless camera installed that is powered both AC and DC.

Just be very sure that all your power cords are ziptied into place so nobody unplugs them.https://www.homedepot.com/p/Frost-King-6-ft-Electric-Water-Pipe-Heat-Cable-HC6A/202262328

I always hear that "if you have a budget, make sure you add 10k to it" Its for all the unexpected things that will come up. 

Not just the standard background/income/asset check, but an unexpected visit to their current residence will give you first hand exposure to what they live like. 

I need you guys to do everything in your power to convince me that I am not and that this is all crazy...

You can make a modest assessment of someone's buying power from this conversation.

Development costs help determine what I developer can pay you for a site.Additionally you need to know if water, sewer, power are easily available to the site and would you need to upgrade all the lines to larger ones to make it work. 4 acres away is a universe in commercial to another commercial corridor.