Well the answer to your questions is yes.
- Export Word to a filtered html and use calibre to create an epub
- Format your word document with BookCreator then build an eBook *
Actually BookCreator essentially does the first step for you. After you format the eBook based on your liking. You can use a GUI driven macro from withing BookCreator to create an eBook for you. In the background it exports the file to an HTML then has calibre create an ebook from there. The only problem is there is no batch file conversion in BookCreator.
I don't know if you're happy with the formatting in your docx file, if you are, then you have a few other options. You can save your docx as an "OpenDocument Text (odt)" book and calibre can convert from there. Or you can save your word documents as a "Rich Text Format(rtf)" and K3 reads that for naively, no conversion required.
Personally I like all my documents to have TOC, chapter breaks and additional formatting so I tend to modify all my books with BookCreator before converting them to MOBI.