A while ago I did something similar. I'm already downloading various playlists via yt-dlp and wrote a web interface [1] to view/play/search them.

My biggest annoyance at the time was importing my existing videos (and converting them to a streamable format, generating thumbnails and hover-previews etc). Do you have any plans of allowing to import existing yt-dlp folder (in the standard layout with a bunch of mkv files, the info.json, the subtitles etc). Because my current archive contains a lot of already-deleted videos :(

[1] https://github.com/Mikescher/youtube-dl-viewer