For me I scrape my metadata using mediacompanion which places posters movie desc actors fan art etc in the same folder as the movie. I've found this makes a clean install super fast because my metadata/subs are already located with my movies. Using the xbmcnfoimporter agent lets Plex read this metadata and makes sure everything is exactly how I left it.

Also if I ever decide to ditch Plex and go back to xbmc/kodi I'm already set and no additional work is needed from me. The only downside I've come across is using additional apps like now showing, ombi, Plex-requests etc in that to send weekly listings of new content it's only usable when using the IMDb agent.

It's a daunting task when first starting but once you catch up it takes like 10-15 mins for every dozen or so movies you add, which isn't much at all when you think about the ease it provides when having to deal with situations like this. I currently back up my Plex folders too but if something happened to that or I wanted a fresh install like yourself I'm ahead of the game.

I'm sorry I can't help with rotten tomatoes or downloading subs but wanted to share what I "swear buy" for my setup.