Be aware in SoCal, you can have sun the entire time, or it can be very wet and cold with rain and even snow at times. It changes from year to year. Just be aware that nights in the desert can drop below freezing. A rain skirt is probably fine. Many hikers only have a rain jacket or pancho. But if you have a rainy spring like 2010 was, you'll likely want some rain pants or the skirt. Beaware, that SoCal can be very windy at times.
As for your pack choice, many have used it. I used a ULA circuit and could have gone smaller but it depends on your gear. A pack is usually the last thing your buy since it has to hold all your other gear with its associated weight. I think the most water I carried was 6L at one time. But that is partially dependent on how many miles you will hike each day (many start off slow to allow their body to adjust). My heaviest packload was in the Sierra Neveda with its long resupplies, the requirement to have a bear cannister, and the need for an ice axe. Some choose to go 10-12days without resupply there but I recommend cutting it in half and resuppling over Kearsarge Pass.
If you are allergic to the blood suckers, I recommend using Permithren treated clothing (either do it yourself) or buy something like Ex Officio's Buzz Off clothing. I only used a Tarp with a headnet or hid in my lightweight bivysack ( both from MLD) but I only camp when I'm ready for bed so I'm not looking for a large netted shelter to hang out inside for few hours before sleeping. You will need DEET no matter what.
You can pretty much make any piece of gear work if you know how to use it properly. But lighter is easier on your body and thus you are less prone to injury. I hiked with a guy who bought most of his gear from Walmart though he did buy a decent backpack from Osprey.
Over all, your gear list isn't bad. The only suggestion might be to wear long sleeves and pants in the desert if you burn easily. I don't think the down parka is necessary. I used a Montbell Ex Ul Down Jacket and just a lightweight Balaclava for the head to sleep in. Never felt the need for warmer covering for my head. But I'm a guy who sleeps warm. The 11oz NeoAir seems heavy and you will run some risk of puncture. Many are happy with just a cut up Z-Rest foam pad. A 3/4 length pad is all you need. You can always put your backpack under your legs if they get cold. Consider using Freezer Bag Cooking and then you won't need to clean your pot.
Yogi's PCT Handbook comes with a large planning guide which includes contrasting opinions on gear from previous hikers (I'm one of them). You might check it out.