Hi Harry
The northern beaches are mainly open ocean if that's what you want. If you want flat water head for Botany Bay. The tide will be good for Dolls Point tomorrow. Come and say hello, friendly bunch down there. Anywhere along the Grand Parade Brighton (Botany Bay) is also OK as long as you are south of Bay Street Brighton. Further north is a No No, too close to the airport.
Next weekend, 27th-28th Sept, NSWKBA is holding a BBQ at Dolls along with the Kitepower Demo day. That's a good way to meet the locals.
Hope to see you there