If you're into spreadsheeting and trip planning (I am, but mostly as a way to fantasize about the upcoming trip ), you might be interested to know that the tables of mileages and locations of junctions and campsites in Wenk's book are available online at http://www.whitneyportalstore.com/data/EWenk_JMT.htm. I did find one error: there are two different locations for Island Pass, about 5 miles apart; the second entry appears to be the correct one.
I think the leg from Yosemite Valley to Tuolumne Meadows is one of the most beautiful parts of the trail, so of course you should start there! Vernal Fall, Nevada Fall, Mt. Clark, Starr King, the Echo Peaks, Cathedral Peak... Yum!
If you've been searching for the best source of information and stimulating discussion related to Spring/Summer/Fall backpacking, hiking and camping in the Sierra Nevada...look no further!