TikiWiki's Categories can only be defined by Admin->Categories, of course needing the admin categories permission, but this is a site wide setting. Tiki 1.9 is the first step into community features, so expect to see this in 1.10 or 1.11
Deleting pages, actually deletes them, so there is no history to rollpage, you can only rollback editing revisions. its not like a undo feature for every action.
As I say the community based, more user oriented control of things is only just starting in 1.9, so sit tight, and enjoy the ride.