3 - The start - I can't imagine not riding away from the border, so my vote would be the 6 mile out n back from the pass as Scott detailed. Any other thoughts from AZTRers?
Sounds good. The consensus is to do the ride to the border, as laid out on the GPS track.
The neutral start makes sense, or at least regroup a bit at the start of the 300. Note that there is a bit of singletrack (it's on the GPX) that is a shortcut over to the start of the 300. It's all road to there though.
5 - Detours - remind me what the detour rules/etiquette are?
I think the only way to be fair is to say now that all the snow detours, as shown in the GPX, are fine. But they are optional. If conditions look good and you want to stick with the route, go for it! More power to you.