I used to live in Qld and can tell you that at this time of year, you shouldn’t need any winter woolies! If you want to be safe, take a light jacket… It can sometimes get cool at night in Sydney, but once you cross the border you won’t need it.
I’m not sure what specific clubs/pubs the tour visits but generally you can get away with neat casual when going out. You will see some girls going totally over-the-top on the Gold Coast and in Sydney… but most girls wear a summery dress and nice sandals… most ‘locals’ even just wear shorts/skirt/jeans and a cute top to go out! You definitely won’t need to dress up for Byron Bay, Cairns, Whitsundays or Fraser Island. There aren’t any clubs there at all!! But I guess it depends on your style and what you’re comfortable with. Personally, I’d pack 2 dressy-dresses maximum and a few nice tops that you can wear to dinner etc as well. Throw in a pair of heels just in case you go out in Sydney or Gold Coast.
Your itinerary looks fun, hope you have a great trip