Starting a bit on the late side, Tehachepi seems like a good place to do it --- about 150 miles to get strong before you climb into the Sierras. I'm not sure that you will need so much water capacity starting from there, but maybe; I do recall getting close to Kennedy Meadows just how amazing it seemed to see so much flowing water for the first time (not counting the pipeline/aquaduct).
I don't think you need long underwear bottoms, though that likely depends on your metabolism. I don't wear them when walking unless it's colder than it normally gets on the PCT, and you just put your lower body in your sleeping bag in camp if it's cold.
Ditto long underwear top; put the windshirt on over your sunshirt when walking as needed. If you need this as a sleeping shirt then so be it, but I wouldn't go for a zip-neck.
Ditto wind pants. Of course you can always send these things home, so at 3 oz, maybe bring the wind pants until you're through the Sierras.
A 15F rated down bag seems a little on the beefy (heavy) side to me, but you know best how cold a sleeper you are; I found a 20F rated bag fine until after the Sierras and then a 32F bag was a great choice from there on. Is it possible for you to find a lighter bag to swap to after you get through the Sierras?
At over 3 pounds that pack strikes me as also a bit on the heavy side, but if you already own it ... so be it, it's certainly not a "bad" choice.
Really, kind of a theme developing here I think --- not bad choices, but not ones I would make. That tent (Nemo Meta) weighs what, about 40 oz? (I always hate when they list "packed" weight vs. "minimum" weight ... I guess repair kit plus stuff sack and stakes total 9 oz. A lightheart solo weighs 27 oz (not including stakes). But if you already own it, I expect it will do fine for you.
I agree with the comment about aqua mira, the drops are cheaper (but you can't buy them in California).
Why a separate camera? iPhone has a decent camera, does it not?
Music player: I think this is a good idea, to save iPhone batteries. A very light unit that works off of a single AAA battery is best IMO, and quite lightweight.
Starting in Tehachepi in June, and based on what we can guess now about snowpack, I'm guessing that you won't want crampons. Heck, you might not even want an ice axe, but that's hard to know. I favor the CAMP Corsa 60 cm. I suggest that you wait until just before your trip to buy one of these --- if snowpack is clearly on the low side, I'd go without it (and especially so if you lack ice axe skills/experience).
Windscreen: easy to make your own; zenstoves no doubt describes this, or you can use Brasslite's instructions: http://www.brasslite.com/windscreen.html
Do you have Yogi's guide? If not, I suggest that you order this ASAP. Definitely to carry the "take on the trail with you" part in sections, but also read through the big "look at this at home" part. Then go out and do a shakedown hike of decent length (maybe 50 miles) if you're able, take careful notes about how all of your gear is working for you. Then read through it (Yogi) again. This somewhat patronizing suggestion doesn't apply (as much anyway) if you're already hiked the AT, but if you're new to long distance hiking then I think a good shakedown trip would help.