I would say go ahead and make a "made to order" listing, and in the meantime you can work on one. When it is done, make a listing for the finished one, and add the photos to the "made to order" listing as well, so customers can see how one book varies from another. Some ppl might prefer to choose the "made to order" listing so that they can have input on the book, like if they love certain colors or something, while other ppl would rather just purchase "ready to ship". But congrats on selling your book so quickly, that's awesome!!!