Not to be a debbie downer, but.... It is risky to take a 16 day river trip with people you have never met and will not be able to meet till the day before put in. Yes, it is a GC trip, and you may view it as the chance of a lifetime, but without being able to meet them in person you are taking a real risk on turning your trip into a pain in the ass. While I have only done 1 GC trip with people on the buzz, it went pretty well all things considered, many things were much harder to do without in person contact with strangers. My 2 other private GC trips were with friends and wnet much more smoothly. I am now planning a GC trip for May 1st with folks from the buzz who are local and already know, after meeting them, it will be a much stronger group. It is all about the people, not just the river, that makes the experience. Good Luck.
May the wind be always at your back,
May the sun shine warm upon your face.