1. Head
(a) rain: Cycling cap
(b) snow: Balaclava

2. Torso
(a) rain: cheap performance plastic rain coat
(b) snow: fleece lined windbreaker (I wear this regardless of precipitation in the winter)

3. Legs
(a) rain: rainpants
(b) snow: rainpants

4. Hands
(a) rain: cold rain: full fingered gloves, otherwise half finger gloves
(b) snow: full fingered gloves like the windbreaker, I wear these whenever it's cold)

5. Feet
(a) rain: booties
(b) snow: booties

- Knobby tires? How wide? If not, thicker slicks? How wide?
I ride 23C tires all the time. The streets in NYC are plowed pretty quickly so you usually only have a day or two of slush.

- Anything else you want to add:

They (DOT or Sanitation) salt the roads like crazy! You'll have to clean your bike everyday when it snows.