At my weight (down to about 315), and riding mostly gravel and crushed stone, I chose to upgrade the wheels on my Trek 7.3 FX, because I am often 7 miles or more from the nearest road when riding my favorite rail trails.

I expect to go back to the stock wheels by the time I am at your weight. I believe the wheels will hold, especially since I get out of the saddle for any bumps or potholes that I see early enough to respond. In the Clydesdale forums are several people at over 200 pounds that ride fewer than 32 spokes per wheel, so it depends on your comfort level. The bottom line, is ride the heck out of the bike for as long as the wheels last, which may be a long time.

I have never cycled there, but Martha's Vineyard looked like a wonderful place to ride based on the one time I did get out there. I'll have to try it some time!