+1 on the Buff, keeps your neck warm but also keeps cold air out of your helmet (if full face).
I ride in over trousers with removable thermal liners, which is good as even mid-December on the M1 I was toasty, and as the temperature rises the thermals just come out. Not used skirt/apron but I reckon trousers would be warmer as there are fewer places for airflow to make you cold.
Personally I don't like the look of skirts and trousers can be warn off the bike if it is really cold!
Some thick gloves may suffice until the really cold days but it depends on how far, how fast and how often you ride, though I may invest in some hand warmers as a few times last year my fingers froze, and that is horrible and painful.
Soldiering on through the winter is character building