I also reached Prime for the first time last casino year so this month's annual tier cruise is my first. I am also UK based - not US - so you may find this useful.
There are Australian Club Royal contact details;
Australia
Toll Free Number: 1 800 965 878
Email: clubroyale@rccl.com
M-F 8:00am – 8:00pm / Sat-Sun 9:00am – 6:00 pm
I called the UK equivalent number and the representative was very helpful. The booking was made under the local (UK) T&Cs and pricing - so pounds rather than US dollars for me. This may or may not be advantageous but for me it meant no port fees and taxes. I believe Australia has the gratuities included in the cruise price so I don't know if you will be given an option to pay them upfront (as I was), will be required to pay them or as they are part of the cruise fare it will be covered by the 'free' offer. If you are interested in an upgrade just ask and they will give you the price which will be the difference between the casino cost of an interior cabin and that of the upgraded cabin category. You can try doing a mock booking to get a rough idea. Some sailings you can upgrade for very little or no extra cost.
Good luck and enjoy!