I swear I'm jealous, even though I live here. for the 2nd September in a row, I'm outta here tomorrow, choosing instead to hike in New England! Best time of year out there as well, far as I can tell....
I wish I had more bike-info for you on the east side, but mtn bikes should not be a problem on the west. There is a short stretch, just south of Lake Ann pass which is legal for dirt bikers, and I did run into 6-8 of those guys when I hiked through there in July, but it was a weekend. They, too were very polite, and the three groups I saw all instantly stopped their bikes as soon as they saw me. One guy even dumped it! I felt a little guilty. I waved them past, no sense them waiting for slow old me to pass. I hope you have fine weather on the west, the east side is looking great for the next 4-5 days at least. Enjoy!
PS: don't OVER hydrate, I see lots of that. Normal hydration is all you need, over hydration does NOT help with altitude acclimation, though under hydration does hurt.