Does Media Organizer keep my LRV, THM, SRT and XML files?

Yes, when they are in the same folder as the recording and named the way the camera names them (usually the same name as the video). Media Organizer keeps them with the recording when you add it to an edit pack, copy it or back it up. In the library they show as small icons after the recording's name, not as rows of their own. See Companion files and exports and Browse your recordings.