Once you've designed the cover elements, I've found the best way to print this onto A4 is to print as PDF, open it in Preview, rotate 90 degrees, and then print physically. I've had problems with shadows reproducing WYSIWYG when physically printed, so I would recommend avoiding the use of shadows. If anyone knows how to totally turn off headers and footers in Pages, please let me know -- Apple's helpfile was pretty useless.
[robg adds: Though I didn't actually print a cover, I did test the template, and it works as described.]

