That's a lot of physical activities. Take note that you cant dive within 24 hours after you landed in Cairns, therefore plan your diving trip on the 2nd or 3rd day.
Did i mention i saw a giant clam which is at least 2m wide in Cairns?
There's too much to do at Cairns, in fact if you a more physical orientated person, Cairns would be better than Gold Coast.
Gold coast only have the theme parks which i would say. . more for family. . .
Cairns is really the place to be at. . you can still go up to Port Douglas.