Google maps tells me 1,420 kilometres away, so, y'know, decently far.
That said I'd recommend you go to Sydney over Brisbane (which isn't where I'm living right now in any case but should be by the end of the year) there's more stuff around there. Brisbane is a cool place to live but really just a stop-over on your way up to the cool stuff in north queensland.
If you're going to come to Queensland you should probably go to Cairns, which is a bit of a bullshit little town but it's the place to go if you want to visit the Reef. And if you come to QLD and don't want to visit the reef then, I'm sorry, but I don't know you (shameful secret: I lived in North queensland as a child and have visited more than once as an adult and never gone scuba diving on the reef, never even went snorkelling till recently).
That said it all depends on what you're wanting to do, there's lots of cool stuff in Aus but a good deal of distance between it all so you've got to plan shit out. I've got mates who live in Sydney so if you're wanting info on something feel free to drop a line. And of course let me know when you're coming anyway. a trans-continental TOUAMBie meet up might just be worth the trip.