21 items?!
Base layer (upper), mid layer, jacket
Base layer (lower), thermal leggings/trousers
Glove liners, merino gloves
Balaclava, glasses (+ helmet if desired)
Thermal socks, winter boots, or shoes + overshoes
That's a maximum of 12 pieces, in this weather I'd be OK deducting the leg base layer if I wasn't planning on being stationary for long.
I was nice and toasty this morning, my toes got a bit numb right at the end, could have done with another pair of socks on, otherwise all good! If you get the weighting of the base layers, socks and gloves right you should be fine!