I'll be hunting argali in early November, would apreciate advice on the following, and anything else you think would be helpful:
-Boots
-Clothing system
-Shooting distances
-Scabbard, stirrups, misc. tack

Most obliged.

Cabelas Alaskan Hunter is my personal favorite. http://www.cabelas.com/cabelas/en/templates/product/sta...ex&indexId=cat601927
If you do a lot of mountain hunting these are great because of the support, right amount of insulation, and the rubber skirt surrounding the bottom of them. They're a bit heavy, but to me it's worth the trade off. I also have a pair of Russell Moccasin Grand Slams, which are wonderful boots but cannot take wet slushy snow for days on end. That said, they are great for mountain hunting. Whatever you get you will want a high top to keep out gravel and for crossing streams.
Clothing. For warmer situations I would just suggest military BDUs, especially the Marine digicam pattern. For later season hunting it is hard to beat King of the Mountain (www.Kingofthemountain.com). For later season I would suggest wool dress socks for your inner sock layer; they will keep you warmer than anything else. I prefer silk long underwear; you can get it from Cabelas. It is light, warm, and dries quickly. I would stay away from "performance" fabrics other than Goretex on boots. My experience is that nothing outperforms wool and silk, especially for stop and go hnting in cold weather.
Shooting distance. 300-450 yards I would highly recommend a rangefinder--I prefer the Swarovski because of its magnification and field of view.
Tack. I actually have a scabbard but have never used it. I've found it easier just to sling my rifle over the opposite shoulder. That way it is always with you. I'm sure your guides will have all the other tack necessary. With hunting boots, thin metal stirrups are best.
Where are you hunting? Good Luck