I would not bring them on the boat. Our trip was crowded and the water was rough. There is no room.
I'd say hotel or car. The office is a hut. The boat was massive though, so I suppose it could go on board with you.
At your risk. There is a space available to place personal items but its unsupervised (mainly) and company not going to accept liability of your luggage. We were asked to even leave our phones in the car. Personally I wouldn't but its your choice.
There is not really a place for that as I remember but you can always call. The staff is very friendly, knowledgeable and helpful.
The place we took off from did not have a building. It was a small boxcar like storefront. You may want to check your hotel or car trunk.
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