Sorry to get to this so late. I have flown to Oz many times. How you'll fare depends on what class you're travelling in. Economy is something to endure whereas business is comparatively civilised.
As others have said, keep hydrated. Comfy clothes and socks are the go. Natural fibres. Wool is the best.
Pack some deodorant in your carry on. Or wipes or something to "refresh" yourself.
Wear flight socks. So important.
If you can, walk around every hour or so.
Take a book and/or spare batteries for toys.
Oh BTW it's Qantas. Not Quantas. (Pedant mode back off now)
Ear plugs are essential. You should get them in your flight pack.
Connections are fine.
Spring in Adelaide. The weather will be coolish - probably similar to a UK Summer. Days will be nice, nights cooler. Further inland you go, the colder the nights will be.
Enjoy the wineries.