Chris,
The plan is indeed to start with a common sub-band for North America. This will maximise coverage initially, and get the project off the ground. We do the same in EU with a single channel plan.
We probably should not be using sub-bands #1 and #8, as they might be used as default by other systems.
Do you have any insight in what a good choice would be? We have been using #7 a bit so far, but maybe something in the middle, like #4 or #5 is better?