I use more or less the same process. Check the book in Word and apply styles (don't care about how the styles look, only the names). Export to HTML (via my macro, so its clean) and import it in Sigil. Since I use styles in Word and have a stylesheet with the same class names, layout is almost fixed. Small touch-ups left and right.
If the source is good, an ePUB is created very fast. If the source is rubish, it can take hours to days to create a good ePUB. The old credo still works: Garbage In, Garbage Out.