The operating system's cmd+` is used to switch between an application's open windows, and that applies to all versions of Pages as well. You can also merge all of Pages open documents into a single window, tabbed interface from its Windows menu > Merge All Windows. That should make switching between open documents much easier.
The Pages application is programmed to expect ⌘+> and ⌘+< shortcuts for zoom in and out actions respectively and changing those shortcuts would likely disable the Pages zoom features. Many have tried changing Pages functionality over the years and have been left with a mess, so I don't recommend changing anything about it.