I can't add to the great list of island considerations posted here so far but I'll expand a little on two items:
1. Which side of an island? We are on the west side of Welch which is subject to the prevailing NW wind so we and our neighbors have the necessary breakwaters. The NW wind often makes docking a real challenge; good boating skills and a well trained and agile crew person are necessary on many days. Also that wind can take the enjoyment out of some otherwise nice days. However we get those unforgettable sunsets and many summer days are fairly calm. On the SE side there is normally (not always) little wind and the sunrise to view but you will have to boat or walk to see a sunset. Our verdict? We will stay right where we are.
2. Islanders by and large are a do-it-yourself lot. Here not only your skills but your neighbors’ skills and attitudes are important. We are fortunate to be part of group of neighbors that have complementary skills, tools, materials and spare part supplies. There will be a few things that go south every year and we take turns helping each other out. Be wary of a camp where the neighbors have never picked up a hammer.
I'll also mention that a while ago there was a thread on what kind of boat makes a good island boat aka floating pickup truck.