Seems like an excellent candidate for a modern USMC amphibious invasion. So it'll need about 20-30 hexes of open sea on all sides.
See if this works for you. I didn't know how much structure you wanted so you can add/subtract from what's there. Also, the feature to the right of the island is my weak attempt to mirror the shoals off the island. Hope it helps as a start for you.
Tom
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