I wear wool baselayers on the AT in all seasons, and it's fine. Really. Yes, the AT is wetter than Montana, and more humid (man, I was shocked at how quickly I dried off after wading around Lake McDonald in Glacier), but very light wool has worked well in my experience.
Your list looks fine. The down jacket is a great idea - I've carried several different models and finally saved up for a Western Mountaineering Hooded Flash jacket. Over a l/s wool base layer it's perfect in March in the Southern Appalachians. If you are starting in very early March, you might consider a microfleece pullover zip-tee for use around camp as a mid layer, or on very cold days hiking. There can be some days when just a base layer and a wind shirt are not enough.
Enjoy the hike. That's a great time to be on the trail.