You can not only use namespaces to organize your wiki pages, you can also organize your media files in namespaces. You can use the same namespace for your media files which you use for your wiki pages (which I would recommend), but you can also create own namespaces for your media files.
Moving and renaming could be done by the move plugin, as I described in your other thread: https://forum.dokuwiki.org/thread/17604
If you open your wiki directory on your hard disk and go to the data/media subfolder, you will see that namespaces are folders on the hard disk. You could rename, move or organize your media files also here. But be aware not to use uppercase characters, and also no whitespaces, german umlauts or other special chars when you rename files, otherwise your wiki won't recognize the files.