A drysuit and good thermal layers is recommended. I've done 4 winter trips both kayaking and rowing, and this is generally enough to keep me comfortable. Second the ditch boots, though some who wear drysuits with the built in booties find them redundant if they just wear the suit for loading boats.
It is good to get some sunny camps now and then, especially for bathing, but I wouldn't obsess over it too much. If the weather is nice, then its all pretty nice, and if it turns nasty, it won't matter that it was supposed to be a sunny camp.
The most important bit of advice is to get rolling in the mornings. The days are short, and daylight hours are at a premium, so get your crew moving and on the water. On my kayak self support trip, we were on the water around 7, and raft trips usually by 9. If you do this you'll usually be rewarded with some sun and the warmest hours of the afternoon in camp.