i now live in canada, but know sydney well. both northern beach suburbs you mention are great places to live! the main place to kite around there is narabeen/colloroy in the surf, so you dont need to go as far as newport to live, although newport, avalon, whale and palm beach are the best places up there (albeit much more $$). peak hour on this route sucks balls. manly is another good option north of the city. the great thing about manly is that its like a medium sized coastal town, only a short ferry ride or drive to the city.
your other good option to kite is botany bay, just south of the city. much closer to the city than narabeen, but def not as nice to live. if you're not against living closer to the hustle and bustle, look at bronte or coogee.
i dont know about kite rental, so do a search and ask the kite shops/schools around the sydney area.
message me if you want my opinion on any other places