5. Re: Temperature Differences in Chamonix Area?
Agree with everything Redzed says. You shouldn't need bulky clothes, you're unlikely to be spending a long time at the Midi. Layers are the best answer - much more flexible.
I run & walk at that level a lot from September - November and this is what I always take:
Merino t-shirt (and sometimes merino arm warmers)
Thin merino zip-up top with hood (or sometimes gilet)
Lightweight down jacket (packs much lighter than fleece and is warmer too)
Synthetic pants (zip-offs are useful)
Wool socks (not cotton!)
Light wool hat or neck warmer/bandanna that can easily convert to a hat
Look out for sales from North Face, Mountain Hardwear, Patagonia etc for down. I think it's really worth paying the money for merino, even if it's just one tshirt or vest. Again, look out for sales. If it's still over budget, try Uniqlo's Heattech. They do thermal vests, t-shirts and down jackets which are really very good at a fraction of the price of merino & down. The jackets especially are great value.
If the forecast is very stable I leave out the waterproof but I always take the down jacket in case of emergency.
I recommend packing a thin thermal under layer as it really makes a big difference if you do get a cold snap. But September is usually pretty nice. Heaven knows Chamonix is due some good weather!!