caplen,
Regarding the Diamox dosage, that's one of the funny things about being a mountaineer who lives in a place without mountains. The doctors are not always familiar with this application of Diamox. I used to live in Houston and I see it here in Oklahoma too. The 500mg 2x daily prescription is not uncommon. Others on this forum have more knowledge than I do, but what works very well for me personally is 125mg 1x daily, unless I perceive the beginning of symptoms in which case I'll take another 125mg. It's effective and the side effects are minimal to non-existant. One note, though, I always include at least some amount of natural acclimatization, like camping one night at 8000' or more and day-hiking higher the day before going in. For me, that applies to hitting the Sierra on the eastside. I haven't been on the HST, but there should be very little worry since the daily route works up in elevation gradually. If it was me, I'd stay overnight in the park at 6000 to 7000' before hitting the trail, but I might consider only carrying the Diamox along in case it's needed.
As long as you stow scented things in the cannister you should be fine for bears. Try not to spill dinner on your clothes, but you knew that.
On summit day from the tarns above Guitar Lake, I've taken two liters of water and stopped to fill-up at Trail Camp. That's been enough for me, but maybe pushing it a little. I like to do the ascent in the dark so I can see the awesome sunrise from the summit (or the notches along the ridge), so I'm not hiking the uphill part in the bright sun. Bringing, maybe, one or two liters more in the platypus is a good idea to be safe.
The warm clothes you mention are good, but I'd probably not bring the silk-weights, and I'd add a fleece or synthetic-insulated sweater or jacket. It might be summer, but it's high and in the mountain weather, so one needs to be prepared. Also, a poncho can blow around in the above-treeline environment where the wind can be strong. A simple rain parka and rain pants can be very lightweight and they are much more effective - they don't have to be fancy. They can also double as wind breakers when it's not raining.
Looks like a fun trip!
