I'm here now and this is what happened.

Once I'd settled in to the hotel, I took a walk down Davies St and found a Rogers outlet. No problems at all - bought 3 sims for $9.99 each and was out of there in 5 minutes. They offered to register and activate the sims in store, but since I wanted to get back to the hotel, I declined after confirming that it was possible to self activate online.

Entered all the details online, but had to try 3 different credit cards - my Australian Visa Signature and mastercard Platinum both failed, but the Amex worked fine. Then, at the end of the process, an error came up saying that it was not possible to activate the sim.

Went back to the store (only 3 minutes walk from hotel) and asked them. Turns out that they neglected to tell me one important thing - if you are bringing your own phone, you need to enter 111111111111119 as the.IMEI and not the real IMEI of your phone. Since I was back there, got them to activate and top up with some funds.

Back at the hotel, I put the sims in and found that all was working great. I had them on the MY5 plan, which gave unlimited calls and text to 5 nominated numbers. Tried accessing data through an application, and an sms arrived with a link to a page to purchase a data pack. Chose the $7 weekly 125MB pass and all was good.

Thanks for all the information.