Sonora is really steep. Tioga is not as steep but is very long and high, and the scenery is insanely great especially near the top. Don't ride in Yosemite valley it's a death trap, everyone is looking at the rocks and not the road. Do go there to hike and sightsee, though, if you are in the area.

I would recommend Monitor or Tioga, both from the west side. Look at the Death Ride web site for info on the passes around there.

Donner pass is nice too. Riding near Tahoe is tricky because there is so much traffic.

34x28 low gear is probably ok, but if you can get the 32, may as well.

Don't underestimate the effects of altitude, you should probably train as much as you can before going.

Do go though, the sierras are beautiful.