I've done this trip/variants a couple of times, and am off next week to repeat.
1. Water sources - last year on 6/7 Sept the following were flowing well: Creek in horseshoe meadows 1.3mi in, Chick spring lake 4.5mi in, creek 0.5mi before lower soldier lake (I took the rock creek trail version of this route rather than the dry dusty route on the PCT to rock creek), lower soldier lake, rock creek (all the way to mile 14.5, guyot creek (16mi), creek in crabtree meadows all the way up to guitar lake, tarns, small trickle maybe 0.5mi after the tarns on the left, small spring at the cables, then the usual sources down the main trail. If you hike the 'true' PCT through rock creek then chick spring lake to the small creek 0.5mi before rock creek is a 9mi dry stretch.
2. Bear lockers are at lower soldier lake, lower rock creek lake, rock creek, crabtree meadows (lower and upper). HOWEVER officially the first 3 of those boxes are only for PCT thru hikers. Clearly this is ridiculous - there are about 3-400 thru-hikers a year, almost all in June/early July, and the PCT does not go to lower soldier lake or rock creek lake, yet the boxes there also have this designation. The idea that a wilderness resource is restricted to a tiny tiny subset of users is somewhat inequitable. I cynically think its all a plot to remove these bear boxes by claiming almost nobody uses them (because almost nobody is officially allowed to use them). The latest draft wilderness plan suggests as much.
3. Depends when in Sept, how cold you sleep, what kind of tent you use etc. etc. I use a warm tent and sleep warm so use a 25-30deg bag for most things.
4. I use deodorant, and used it for a whole PCT thru-hike. Makes a big difference to smelliness.
5. I don't carry in the Sierra, even when hiking with kids.
