Starting with the DOC file (DOCX) is certainly the way to go. If you want it in one step then I would suggest
Atlantis Word Processor as described in our wiki. It has a built in Save that can create an ePub. It is forgiving if you don't name your paragraph styles (nameing them is still better) and will assemble them for you by collecting the same formatting under one CSS style. It also provides features like adding a cover, setting margins, etc.
Dale