>Don't need to worry about transcoding on the fly because I make sure all video files are in H264 going in, which can be direct-streamed to pretty much all clients.

That doesn't work if you use subtitles. With many formats, the subtitles have to be transcoded on-the-fly into the video, even if the source and destination resolution and codec are the same.

Also, the Intel NUC might be fine just running Jellyfin (without transcoded subtitles) using separate file storage, but if you try to combine that with a NAS box running 4-8 drives using ZFS and perhaps a few other services as well, it's probably just not enough.