If you're building exclusively for iBooks, you're probably better off using iBooks Author and avoiding messing with the markup at all.
Incidentally, the one-page versus two-page spread depends on the orientation of the book and on whether you have set the orientation-lock option in the com.apple.ibooks.display-options.xml file. See:
http://ebookconverting.com/working-w...-format-layout
for details, or download a copy of the iBookstore Asset Guide.