I think you should look at the Starboard Phantom 320. At 320 * 71 is is long enough to have some lightwind glide, and wide enough for stability. It will work well in most wind coditions (and will be pretty fast in a breeze), and be enjoyable as a cruiser.
Sail size is of course harder to tell, it depends on your weight, physique, and wind conditions. Maybe a 6 m2 freeride sail would be a good strating point?