It shouldn't be cold as most of us define it, but could be cool on the first few evenings. I wouldn't go overboard with packing a lot of heavy clothes. Maybe a windbreaker and a sweater at most. I'd pack more long pants than shorts. In a way it's like packing for an Alaska cruise.
Seas? No way to know. That is the time of year for cold fronts to cross North America and head out to sea, so it would depend on that happening as to whether you had some wave action. In the Navy I've been in the middle of the Atlantic and had almost glassy seas one day, 20-30 feet seas the next. And of course, it will still be hurricane season.
As for me, I'm waiting until you bring the Liberty over before I board in February for a B2B of 9 days total time (4 night Rock Legends Cruise followed by 5 night regular cruise).