a. No opinion on Onion Valley. I heard it is beautiful and has some very nice hikes. But I have never been there. The extra altitude can't hurt.
b. I'd go for consultation lake just short of Trail camp. But it is pretty barren up there...no trees.
c. Last year I drank 2L between the switchback springs and the summit. 1/2L from the summit back to the switchback springs. I'm twice your size and I was taking diamox (62.5mg x 2). I was not dehydrated.
d. Don't know the guidelines on packweight vs bodyweight. I'm sure I could carry 60lbs, but I certainly wouldn't want to. I got my pack down to 30lbs on my recent trip to Meysan Lake.
e. Food...everyone will say, bring food that you know that you like. It isn't a good time to experiment with foods. I personally like foods that are nice and moist..on the wet side. The air is dry up there and dry foods can be hard to get down (I did a lot of sip and swallows).
f. Last year I went up 9/6-7. It was right around freezing at trail camp. The wind starting at trail crest made it pretty damned cold up there. I had a 32F bag last year. It is possible to have true winter storms on Whitney at this time of year. My reaction to last year's trip was to buy a 15F bag for this year.
Hope this helps....and of course, there are other opinions that you will likely hear.
