Okay pardon my ignorance. So then designing it on Wordpress would be better than making it a straight PHP site right? Because you can manage it easier without sacrificing customization?
It depends on the amount of customization you'll need and your level of PHP knowledge. I often build my CMS-es myself, because I find it easier to customize rather than searching or writing Wordpress plugins. But if you are not a php programmer, then of course choose Wordpress.
My vote = install WordPress and go from there. It's a robust platform and will provide you with everything you need (usually only a click/plug-in away).
You should go for wordpress because it is already good CMS with lots of plugins to extend the functionality. But maybe learning PHP and creating your own CMS will pay you off better in future.