One thing I haven't seen mentioned, and it's going to count a lot, is what is your physical shape? How much packing have you done?
I have two months to get ready. I started hiking portions of Palomar Moutain which goes from 700 to 6000 feet or so. I do as much as I have time for... every other day. I am going to go with a full pack and climb the full portion several times before I leave for the Sierras.
I used to backpack with my dad & brother every year in the Sierra Nevadas when I was a teenager. I have also attempted Mt. Shasta (14,000 feet & change) a few years back. The Shasta trip was new to me... all activities were done in the snow and ice....hike, sleep, eat, etc. I took my Glock #22 up Shasta. I froze my a$$ off at night and learned a lot on the Shasta trip.
I have some friends who also want to go on backpack trips. After this trip, I will be going on more. I want to get back into the backpack thing.