Hi 63!
Last year on the second day of my JMT hike, I took a wrong turn and ended up on the Clouds rest and no regrets though! I can answer some of your q. I came down towards Tenaya lake on that trail and fortunately found a 2 mile branch trail heading to Sunrise camp where I was originally headed that morning. There are at least two streams flowing in that dry year. So you have water after 2 miles into the hike from Tenaya lake TH. Since it was a new trail for me and am running out of water on my descent from CR, I was anxiously querying hikers coming up and they assured me that there are lots of streams in between.
Before starting JMT from the valley, I also stayed in Mammoth for acclimatization and it did help. The 1.5 hrs may not work depending on any one way traffic issues (due to road construction or due to some heavy slow moving trucks). So keep more time for those uncertainties unless you are driving in the night, in which case be wary about deer and other animals crossing.
North dome is about 9 mile round trip and downhill hike to north dome with excellent views! Very easy!
