I want to thank everyone for their comments - I'm taking all of your advice and going business, maybe first if I can swing it. As it happens, we may all end up on different flights so it's less of a big deal than I originally thought it might be.
As far as the other issue, that I haven't traveled with his group before, I'm not concerned. It's not the "trip of a lifetime", I've had other, fabulous travel experiences that I don't expect this to surpass. (It may, but I don't have such high expectations.). And, if I find the others annoying me, I can see myself ditching them for some solo travel. I was planning to do a 40th birthday trip on my own, as I find myself single these days, until this opportunity arose. Life is always full of surprises, isn't it?