As the previous post says, Dolls Point is the main beach in Sydney for beginners / intermediates. It does get crowded on weekends, but generally during the week it is much quieter. About an hour and half south of Sydney is another great spot called Windang Island. Large crescent shaped beach with plenty of space for launching and never very crowded.
Check out this web site (scroll down past the picture..) for a list of sites around Sydney..
http://www.australiankiteboardingschool ... ations.htm
Nearer the time you are due to arrive, drop me an email and I can give you some pointers..