I just installed both Sonarr and Radarr about two weeks ago and I can honestly say I truly must of been insane not to have done it a LONG time ago. Both are truly sweet. Sonarr has all my shows, and radarr I just keep movies in it I haven't seen yet. I'm no fan of Kodi cause in certain Linux distros it adds itself to the user selection during boot. That would be fine if I had a dedicated Machine hooked to the TV, but for my main machine it's a bit annoying cause I like to reboot and know the system will land back on the desktop without me having to select which user to log in. Plus there is the fact that at least in Windows Kodi when you click to end Kodi it takes forever. For media to the TV I've been happily using Emby.  The only thing I really need for this system is to finally upgrade from the Ryzen 4 3200g to the Ryzen 9 3900xt. Then I can go back to transcoding my shows and movies any time I want instead of only doing them while I'm sleeping. 

Both Sonarr and Radarr are indeed sweet 😊  - a reason why I do not use Rename My TV Series that often anymore myself.

For Kodi I use an nVidia Shield (Android) and a tiny dedicated PC running LibreElec. Both run smooth, but I can see why you wouldn't want to run it on your system this way. I didn't even know Kodi would do this, but I've always ran Kodi on a dedicated machine.

It's been a while that I looked at Emby. I did want to try Plex a few times, but I hate the mandatory signup and the "sharing" of information. The Plex user agreement reveals that your filenames and media info will be shared - not something I'd want. And Kodi works great the way I sue it. 😊 

Why not upgrade to the new AMD CPU's (5000 series)? They are likely compatible with your mainboard. I read that the AMD 400 and 500 series chipsets are support, and that quite a few boards with the AMD 300 series chipset will get support as well?

 a reason why I do not use Rename My TV Series that often anymore myself.

both rename well enough to not need RMTV? Show (yeer) S??E?? Episode Name, Movie (year)?  SAs for upgrading to the 5000 series I've done the numbers and the 5800x runs about a 100 more than the 3900xt and the 3900xt actually beats the 5800x in performance, not by much but does beat it.  That and not bios upgrade for it yet. As for a dedicated machine just for media hooked into the TV I just need a case and better video card cause I have everything from the AMD 3 6300 system. The card on that system is a nVidia 750ti. It will handle the 60 in 4k TV but that's the high end of what the card can do, and I'd be more comfortable with a card with more power.

Well, Sonarr (for TV shows) oes rename flawless so far. I only need it for the odd files that I get from outside of Sonarr.
Year is included (I suspect always), S??E?? works, and separate folders per season, works well.
Radarr does a pretty OK job as well, but I'd recommend using Tiny Media Manager for movies.

The 3900XT is indeed an interesting processor and it sounds like you've done the math already 😊  
I'm thinking of building a PC early next year (when certain components are actually available 🤣 ) - the nVidia 3080 and one of the AMD CPU's are on the list to explore. We will have to see how things develop in the next few months before I decide what to do.

Movies I don't get enough not to simply do it by hand based on TheMovieDB naming. As far as taking my old parts and building a dedicated media box I think a Vid card with twice the processing of the 750 should do very nicely without breaking the bank. Just have to find a nice looking case that lays on it's side.