Known for its 250 square miles of flats fishing, Deep Water Cay heretofore has been a small community of only seven privately owned homes, seven cabana units, and four guest cottages (packages starting from $1,000 per night, per person, including lodging, meals, and activities). But this fall, the 55-year-old private island resort off Grand Bahama’s southeast shore will break ground on 53 new waterfront residences. The two- to five-bedroom estates will be offered as privately owned, furnished homes with prices…