I don't specifically remember what color band we had I think yellow, but it seemed to be very random. They just came around and gave you one, the two groups just needed to be even.
As far as what group went first in the encounter vs. on the beach again it was just random, the guy running in looked at the people standing closest to him and said, "OK we'll start with the yellow group" and so the orange group was sent to the beach for the morning.
I really liked going first, but I don't think it really would have altered the experience much, I just liked relaxing on the beach afterwards. It was spectacular.
Hopefully you will have time to shop, I think because it was so new the timing and switch off schedule wasn't really in place yet. Also the fact that Disney doesn't really run this, Dolphin Fantaseas does.
Enjoy, it was great!