The plane will be a 737, Ive done SYD>Ayers Rock in Y and it was fine but we did have a spare seat between us. We now fly J, because we can
You can buy single day access to the lounge in Sydney to shower and rest after your flight. I think its $65AUDpp
I think $500 each is rough for this flight - would buying a comfort seat in economy be a better option so you can at least have the row to yourself?
Meal wise, I think in Y you get a drink and snack, depending on the time a snack could be anything from a cookie to a wrap. In J you will get a better meal.
Have you checked expert flyer, is the flight full?
Edit: BTW. When are you flying? Join and join-in the Aust FF forum as there is a lounge meet up thread. If you are a regular, someone might guest you in. Im guesting someone in next month.