I use a rPi3 for this stuff exactly. I have about 300 movies in the folder (I know it sounds like a rookie number but I keep only stuff I know it will be watched) and kodi (through jellyfin addon) only takes a few seconds to load. My jellyfin server is not on the nas itself, it’s on a separate docker server for hw transcoding on the fly (and the nas has hdd drives).

I used the piped addon for youtube.

I use kore app on my phone to control kodi. Been working like this for about 7 years.