Australia - high adrenaline but laid back experience?

[kerk]

Its summer now. Im from Sydney, and i think Josem is right though, Cairns/ Brisbane/ Gold Coast are all great area's for the activitys you have suggested. Sydney/Melbourne tend to have those things but have more of an expensive tourist attraction sort of hyped up feel to it.
Nightlife without question is best in Sydney/Melbourne but for the things you suggested, QLD is your best choice.