1. Canisters...A nominal fee. If they are out head to the Hostel in town. They are usually less expensive.
2. How many Canisters...For an overnight the way I pack, 1 per 3 or 4 people. The way most pack 1 per 2 or 3 people.
3. Zip or unzip...I leave the tent zipped and packs unzipped. I have never had a problem. However, I have seen a bunch of tents blown to hell and back because they were guyed out and the wind came up. It ain't no fun looking for your tent at the end of the day.
4. August Temperatures...It depends, the coldest night I have spent in the Sierra has been in August at under 10,000'. I've seen <10 F on the summit. I've also had >50 F overnight above 10,000'. Check the California Water Resources Board's Cottonwood Lakes Reporting Station for historical temperature data.
5. Cold...A cold front passing through is not your friend...unless you have the right clothing. Yes, it gets that cold regularly. It just depends on the day you hike.
6. Alternates...Screw alternates, you got the permits. If you have the clothing go as far as you deem it safe. You will have a good time.
