I’ll be back in England by then mate. Yeah the classic backpacker route is the east coast, would recommend doing the Whitsunday Islands and Frasier Island, both absolutely amazing. Sydney is great, let me know how long you’re there for and I can give you some info on stuff to do if you need anything.
Having not been to Canberra I don’t feel like I’ve missed anything out there, as everyone says it’s shit
Perth/Fremantle is nice for a visit, lovely beaches and has Little Creatures brewery
Definitely look into the East Coast, so much to do.