[Casseres]

First of all, owning an island sounds awesome. Congrats on making the leap.

I don't know how much knowledge you have about desalinators, but here is a FAQ by the company that makes the reverse osmosis unit that I use at work: http://www.searecovery.com/marine/src_faqs.html Being so close to land, you will need a way to sterilize the water. A UV attachment should work.

I also recommend taking a course in Wilderness First Aid. I took a 70 Hour Wilderness First Responder course by Wilderness Medical Associates. It was an excellent course.