If you want to test how the formatting will look as a Kobo ePub (KePub), you can change the filename extension of the book from .epub to .kepub.epub before copying it to the device. That will cause it to be opened with the KePub reader instead of the Adobe ePub reader. Some things like highlighting and reading stats won't work properly, but it will give you an idea of what the formatting of the book will look like.
This should be all you need to add to your stylesheet to avoid the unsightly gaps at the bottom of the page in ePubs:
Code:
p {
widows: 1;
orphans: 1;
}
Edit: And beware that the KePub reader completely ignores page-break-before and page-break-after styles. The only way to force a page break in the KePub reader is to begin a new html file.