I second the above said by Rainbow. Living in Alaska with winter temps sometimes down to 30 and 40 below zero Fahrenheit, I’ve never once used a jumpsuit. I don’t own one. Climbing Denali most people don’t use them. I didn’t. Maybe Elvis did, he had a few.
Anyway - your best bet with clothes is layers for sure. Your pack’s weight ain’t gonna be ultralight in winter and that’s awesome 'cause you’ll know you’ll have what you need. You won’t be facing deathly Alaska-like temps so you can probably get by very easily with:
lightweight thermal pants (Duofold, Patagonia, REI, etc)
standard nylon trekking pants with zip-off legs
you ought to know your body well… unless you’re a lover of hot temperatures, some days you won’t even need the thermal underwear with proper upper body insulation.
My personal tolerance level is I can wear shorts down to 40° without much wind, pants of some sort without anything under down to 0°, and with wind on a trail you should have some lightweight Marmot Precip-type pants which you can throw on at a moments notice. Those will also be just fine in any snow you encounter.
Only the very coldest days you’ll want the thermal underwear (but certainly a clean (or semi-clean) pair to sleep in.) You’ll wanna carry at least a small key-chain size thermometer to check how cold it is each day to judge whether or not you wanna wear the thermal underwear (also know what elevations you’ll be at 'cause of course the higher you are, generally, the colder it is.)
Some days in some places it won’t be super wicked cold… a lightweight long-sleeve base layer would be my pick for what I throw on first in the morning. a 2nd layer would be a midweight fleece top, then a midweight fleece jacket. I’d also have two other items: a heavyweight fleece top to replace the midweight top in case it’s wicked cold. Also: a Marmot Precip-type rain jacket with hood which’ll, again, do just fine in any amounts of snow you see (unless you’re gonna go sledding then you’ll want true snow pants and jacket!)
Truly a jumpsuit (again, unless you’re gonna go sledding) isn’t needed. Layers!
And, of course, in winter you should be with a good pair of hiking boots with Gore-tex, no lightweight, summertime sneakers many ATers like.
Starting in January should be awesome!!! I’d count on more trail towns than you might be thinking. After a few days in the cold… in the constant cold… a hot shower in a motel/hotel will be like heaven and you’ll be refreshed and ready to hit the trail again. I’ve known hikers in winter to take a couple days here, a couple days there in places like Gatlinburg just kickin’ back and enjoying a warm bed, hot showers, movies, TV, pizza, hotel jacuzzi all before hittin’ the trail again not to have a shower again for a couple weeks.
ENJOY!!!
I Don’t Believe in Trail Names
