Are you only going to have 2 wires going around the wrist? I'd recommend you rethink this. At least 4 wires in order to anchor the stone well, for one thing. Also, to give the bracelet more body. Re: gauge, I'd try 16 HH. By the time you're done working it, it should be work hardened enough to hold its shape.
Hope this helps,
JoAnne