1. Head
(a) rain: helmet
(b) snow: neoprene "beenie", helmet

2. Torso
(a) rain: whatever, warm highneck wool sweater, gore-tex cycling jacket
(b) snow: whatever, warm highneck wool sweater, gore-tex cycling jacket

3. Legs
(a) rain: - shorts over tights
(b) snow: - shorts over tights

4. Hands
(a) rain: - full finger gloves
(b) snow: - lobster claw gloves

5. Feet
(a) rain: - socks, leather shoes
(b) snow: - socks, milk bags, leather shoes

- Knobby tires? How wide? If not, thicker slicks? How wide?

25mm slicks. They're garbage on hardpack. Consider some cyclocross or studded tires, or just learn to ride on what you have.

- Anything else you want to add:

Get a fender, at least for the back. You'll look like your ass exploded otherwise.