Well, I guess we are talking about the same OZ Experience unless STA travel has it's own program ;-) If you go on the website (http://www.ozexperience.com/) you find some example itineraries. There are quite a few stops along the east coast and the 20 day itinerary Cairns - Sydney looks quite good. Sailing in the Whitsundays is awesome. I loved 1770 (Agnes Waters) and also did a kettle station stop which was a great fun. Fraser Island is also great. The biggest sand island in the world. Although the Gold Coast is not on that itinerary, if you should stop here let me know. Besides Surfers Paradise we have some great beaches and rainforests. And yes, Byron Bay should definitely be a stop.
Regarding how it works, they also have a section on their website about this. I remember that the driver had some brochures on the bus and did the booking of the sailing trip for my while approaching Airlie Beach. I usually stayed in hostels and there are be quite a few along the way. Call them one or two days before, once you know when you will be there. That usually worked for me. You can also find a bus time table on the website. Busses usually don't come through a place everyday, so you just have to see if you for example stay 2 days until the next bus or wait for the bus after that. I think you just all them to make your booking (tell them when and where you wont to hop on or off) and that's it. May sound complicate, but once you are on the bus and if you have enough time, then it's quite fun and easy. 