G'day Chrisophe, Welcome to Aus. Pitty you came in winter where the wind is not so great. You will be lucky to get a kite in once a week.
A good place to start meeting people is through
kitesurfing.com.au/ The site is run by a top bloke called Rob, who pretty much connects everyone on the northern beaches and also gives great updates on the weather conditions.
The locals on the northern Beaches are all very friendly bunch, the only things to watch out for are; make sure you stay well away from other beach users and becarefull kiting in Longreef lagoon, its full of junk that will cut you or your kite up.
Beaches
Narrabeen N, NE
Longreef S,SE
Hope to catch you out on the water mate.
Alex