It is nice to connect with others who will be diving. I think there may be a dive master on the cruise with us who starts the very first day with lessons for those who need them, not sure how the dive spots are chosen and/or how different groups get to them. In the caribbean, the dive spots are marked as 'beginner' or 'advanced', not sure what this denotes, whether it means depth or complexity of the dive somehow?
Re: barrier reefs, I read online that the second largest barrier reef in the world is in Tahiti, not sure if we will be close enough to dive there during the cruise. I also don't know if you can snorkel just as easily or if being able to dive gives a significantly better experience, will have to do some research.
I'm also thinking it would be nice to visit australia while down in that part of the world, and wonder if september is springtime? Still cool, or a nice time of year?