I know its already been mentioned but once you get organised go and see the boys at Windsurfnsnow, they can give you all the info.
Just quickly.................
Southerly winds, try Long Reef, Makaha, Newport reef, Palm Beach and Sand Pt on Pittwater.
SW, try Long Reef, Narrabeen lake and Pittwater side of Palm Beach.
W, really only the lake works, Pittwater but gusty.
NW, again see above.
N is pretty much crap.
NE, Palm beach, certain spots along Narrabeen/Collaroy strip, Long Reef if your very lucky and the lake is always an option. the wind funnels and is usually stronger than the beaches. water is questionable in summer but its a sail.
Go to the western end near Academy of Sport.
Still, its a beautiful area, top surfing and friendly locals.
Have fun