I personally prefer synthetic clothing insulation layers, because my sleeping bag is down and I hesitate to put all my insulation eggs into one basket, so to speak.

Here's mine, for the Wind Rivers this summer, where the weather is even more likely to be as Jim describes--and yes, all the layers can be and have been worn all together:

Capilene 2 zip-T (used as hiking shirt)
Nylon hiking pants
Capilene 2 baselayer bottoms
Merino wool T-shirt (short sleeve)
Wind shirt, Montbell UL
Montbell UL Thermawrap jacket
Rain gear, Brawny Gear silnylon jacket and pants
Manzella polypro fleece balaclava (it's really important to have something to keep your head warm--"if your feet are cold put on a hat")
Manzella polypro fleece gloves
Mountain Laurel Designs rain mitts (shells to keep the gloves dry)

Plus a Western Mountaineering Ultralight Super sleeping bag (20*). I also carry a pair of 200-wt fleece sleeping socks as well as a spare pair of hiking socks.

You may want to consider long sleeves and pants for hiking plus a good hat for sun protection. The sun is fierce at high altitudes and sunscreen can do only so much.

As Jim says, altitude is important. I grew up in Wyoming and Colorado, but have most of the last 50 years at or close to sea level. I found last summer that childhood acclimatization definitely does NOT last forever! I got really tired, lost my appetite and as a result definitely had less resistance to cold. Short easy days the first few days of the trip are definitely a good idea!