Sounds like a ton of manual HTML work. You might want to consider using the
CustomerCleanerPlus plugin which will thoroughly clean out either an imported HTML file or an epub in Sigil. This plugin does two things -- it will clean out all the dross, redundant code from the html as well as do its best to ensure epub 2 HTML compliance. This plugin is an epub-specific cleaner. It also has lots of other options as well, which might be useful to you.
All you have to do is save your Word doc as
Web Page HTML(Filtered) and import that into Sigil. Then just run the plugin. This plugin also cleans out standard epubs in Sigil as well.