Apres-ski: Both towns are pretty laid back and outdoorsy, Taos much more so than Santa Fe. So you can go pretty casual. However, both towns are artsy, so you can go with just about anything, though furs probably would make you stand out!
Wear what you're most comfortable in and have fun!
Not sure what you'd see on the slopes, but knowing most western resorts (except for Vail), technical ski wear (a shell over a fleece or a down sweater), technical pants (Patagonia, Mountain Hardwear, Arcteryx)...is probably a better choice over skiwear designed more for style. And, you'll be able to adapt to changing weather conditions more readily.
And, if you have dinner in Taos, you must eat at The Love Apple. It's a fairly nondescript looking place on the right-hand side just a few blocks north of the plaza (past the road to Taos Pueblo). Some of the best food I've ever tasted, I've eaten here.
I spent a lot of time in Santa Fe and Taos this past summer. Santa Fe will be my summer home for the next few years.
Unfortunately, in the winter, I'm mostly stuck in PA except for a few short escapes.
My favorite mountain? Unfortunately, I haven't been to a lot of western resorts (though I seem to have spent most of my summers in the west for the past 20 years)...Winter Park, Copper, and Alpine Meadows come to mind, though.
In the east? Whiteface. That place just feels like home to me.