if you're able to post the error messages you were getting from iTunes Producer it would help to compile a sort of workflow or checklist like you mentioned.
i'm not sure how popular a word > calibre workflow would be, though, because word generates a huge amount of messy code, and i imagine that how calibre interprets various forms of Word-mess could vary widely from book to book.
i think a better idea would be to use Sigil or InDesign to create the epub. both create cleaner code than Word, so it's less likely that you're going to have upload problems onto retailers' sites, and then it's just a matter of decoding the error messages that Apple is giving you. in my experience it's usually it's something a missing reference in the <guide> element.