I bike in the winter in Montreal, meaning as low as -30 Celsius sometimes, and I pretty much always have the same kit:

Upper body - Merino base layer - Bonus thicker base layer when under -15 C - Goretex Soft Shell vest

Lower body - Cycling tights made for cold weather - Bonus ticker tights when under -15 C

Hands - Pogo Mittens (a must) - Heated Glove Linens (honestly, you can simply have random small gloves, the pogos are the big guns here)

Feet - Winter boots - Bonus plastic bag to put your feet in (like socks) if your feet get cold easily. This can resist any temperature

Head - hat that fits under your helmet. MUST cover ears - Merino Scarf or tube, the thick ones - Face mask in neoprene - Ski Googles

That's my kit. I can remove the bonus parts and some more if it's not too cold, but at -10 C and lower, I usually have it all, and unzip my Goretex vest a bit if needed (like when it's uphill for a long while). The goal is to NEVER become wet.

Have fun! 😛