I really like Zonx's idea for managing the two modes of display. This seems like a pretty good way to allow modders to arrange the controls in any way they want. I didn't even think about the targeting yet so I'm glad you brought it up. It certainly makes sense to limit the targetting to the basic page or even have a targetting page that sits on top of both of them. This would allow you to place it over any of the controls you want.
As far as setting the Volume.CellSize = to the basic or advanced pages. These pages would only be large enough for 1 group member unless we make them much bigger than they need to be, but that would look messy. One option would be to make sure the basic and advanced pages are exactly the size you want for 1 member so that CellSize would equal the width of the basic or advanced page and the height would be 6 * the basic or advanced page height.
Let me know what you think.