Cortez is definitely not far from the action. To get to the island from the seafood shack, you would need to cross the bridge (it's not a bad walk, or you might be able to take the dinghy to the island side of the icw?) and then you can take the free trolley anywhere you want to go. The whole island is only 7 miles long, so everything is pretty darn close.
The city of cortez itself is cool too, with a fisheries preserve, funky restaurants, and the maritime museum Maritime Museum
The best fish markets are in Cortez as well.
The north end, city of Anna Maria, is my favorite place, very homey and laid-back. From the cortez bridge, it's 20 minutes on the trolley, a pretty ride, and folks on the trolley are always friendly. There's a marina up near Rotten Ralph's, but I've read that it doesn't allow boats under 40'?
You'll love it.