Found this on the CustomPress info:
Pay attention to the above: You cannot move content around after it has been created so you would have to delete and re-enter. In most cases you probably should not network activate and activate locally on those that need CustomPress.
So you can activate it only on certain sites? I thought the only way to do that was by using Pro Sites.
More important questions:
Since Marketpress comes with a post type (products), can I just add custom fields to that, or should I use Custompress make a whole new one? I think I just need one post type.