We did the Vancouver roundtrip itinerary last July and loved it so much that we are doing the Seward-Vancouver itinerary this July. It is an amazing trip! Windstar can provide transportation to Anchorage, but you will need to make reservations and pay for the transport. We are using Windstar transportation to get from Anchorage to Seward the day of embarkation. There is a beautiful train ride that you could take instead.
Definitely take a parka, rain gear, hat, and gloves and some sweaters and/or polar fleeces. The weather is unpredictable but can be quite cold and damp. I only wore shorts one day. Layers are the most practical way to go.
Passengers in the dining room still dressed in a "casually elegant" fashion, with slightly more emphasis on casual since many wore sweaters.
I didn't notice the ship being especially cold, but that could be because I was wearing heavier clothing than usual.
The only meals that were noticeably crowded were lunches in the Veranda, especially if the weather was too cold or wet to sit outside. However, you can also eat lunch in Amphora, which is very nice and has plenty of seating.
The Expedition Team really helped make our cruise memorable. I highly recommend you participate in the excursions that utilize them.