Editing can be difficult if you have no idea how to straighten or clean up a image in Photoshop. Removing scuffs and dust particles on pages is also required. Merging double page ads together to look seemless as possible. It comes down to if your committed. Also time consuming. A mag can take weeks to fix up.
I would start on a cover and see how well you can clean it up. I cant help you with Japanese mags. Maybe ask a forum member.