Can I post an item, and pictures of it, in my Shapeways shop as not for sale, but still buy my own product to sell it in another site? Example; I may need 25 pieces of a sculpture as a Kickstarter reward, but I don't want people buying them anywhere else.
Yes, you can. Just edit the model and turn off "Offer for sale to others". The public won't be able to purchase it, but you can at any time.