I hope you found this site before you started buying all your gear. I didn't, and ended up replacing a lot of the stuff that was marketed by REI and the like as UL, but in reality is barely worthy of the name lightweight.
This isn't a book on the JMT, but I went snowcamping with this guy last winter, and he's doing his 9th JMT hike this summer. Here's a youtube on his hike last year if you want to see some highlights.
Yosemite is great, but if you find you can't get permits for your desired dates, know that there are a lot of great locations that require permits but have no quota's, so you can go last minute. Powell Lake and Y Lake in Emigrant Wilderness are a fairly easy 2.5 and 5 mile hike from the trailhead, respectively, and make great starter trips. My girlfriend doesn't backpack, but if I could convince her to try it for one night, I'd take her to Powell Lake. Also Granite Lake in Mokelumne Wilderness is only about 2.5 miles from the trailhead. Neither place is much farther from SF than Yosemite.