For one of the lists I'm on, I put together a couple pages as an overview of how to format a book in doc format for BN or Amazon. If you want a PDF copy, email me and I'll send it to you.
Remember that BN takes uploads in doc, docx or epub. It does not accept zip files. It doesn't need to. It's fine with images in your document as it is. (How about getting with the modern era, Amazon?)
Amazon takes doc (not docx) but it's happiest with html. IF you have any images (like the cover) you will need to convert your doc into html. Then you will have to create a zip file making sure you have all the image files and the document in html format in the zip file.
It's good if you have an html editor program to check everything one last pass. I had trouble with the images linking this past week and had to go in and manually change every one of them in Fling this week. Make sure the document is looking for the image with its correct appellation. It'll probably be renamed to something like image001.jpg. The document is probably going to be looking for mrsawiggins.jpg so your image won't show up.
I use Expression Web for all things html/web work and I'm very happy happy happy with it. I used Dreamweaver for a while and it made me nuts but maybe you'll be better with it. I don't know what Sigil does. It seems confusing to me so I never keep it open long enough to find out. Expression Web is not confusing.
I have no experience uploading a mobi file to Amazon--sorry.
Here's a chocolate tart I made yesterday for the NLM2 book.
I'm discovering something about me and food photography. It's a still life. I'm not there to sell the food. In this image, I'm more attracted to the verticality of it than I am intrigued by the chocolate tart.