Here is what I suggest.
Separate each chapter into a single XML file. That way you will have full control over how the chapter header will look. Also, it will help you conform to the mobile ADE standard which is needed for readers.
In the CSS in the body style add in...
Code:
body {
windows: 0;
orphans: 0
}
This will turn off orphans and widows and make things a lot more uniform.
Since you are using Word, you may have to go into the ePub and clean it up to remove the code that Word adds in that's excessive or incorrect for ePub. For example, all the font family in CSS that have no use. And other things.
Make sure your code validates with FlightCrew. After that, view it in ADE and see how it looks. Make sure your external ToC has all the entries needed for a proper ToC.
Also, make sure the margins are not too large. 5-10px left/right at most.