Ah, a Sorrel snob. So many of them cos no one sells decent snow boots here
Try Kamiks and tell me when you are selling your Sorrels. 1/3 the price, half the weight, superior performance.
Though you wouldn't notice in an aussie "winter" anyway. ;P
My 2c on the gear- all of the above is relatively accurate and will keep you warm. I'd do the single layer and huge coat thing if you are mostly idoors, or being very active outdoors. Of course those jackets would be different. I'd go a puffy down for city/non rainy stuff.
I prefer 700-800+weight down but this is just the loft, not the insulation. Make sure it has a goodly amount of down actually inside it. 10g of 800 loft ain't got anything on 100g of 700, it's what many people don't realise. The difference is in how light it will be for given Xg of insulation. Higher is lighter.
Above roseanna said waterproof should be wind proof. Completely wrong, things can easily be one or another or half half. They also trade off breathability unfortunately.
-10 isn't too bad, it all comes down to the winds. I reckon you'll be ace in a good downie for nowhere near $1000, esp if you can find a sale. Marmot make decent gear at a lower price. And the absolute best- Alpkit. You will not beat their price:quality ratio, similar quality to cheaper brands but about 25-30% of the cost as the direct sell, no wholesalers (outdoor gear markups around 100% or so in AU).
