FWIW... I use Spotify quite a lot, and when I first open the app, I'm immediately presented with pre-curated playlists that seem to cater what I might need at that time.

On a Sunday morning, I get 'Sweet soul Sunday' or 'Easy Love Songs'. At 9am on Monday it's 'Concentration Music' or 'Background Synth Songs'. Around 2pm, you start to see 'Workout Mix'.

Then you have 'Daily Mix 1', 'Daily Mix 2' and so on which are automatically created playlists, based on what I've listened to. They themselves are generally categorized into rough timbres or styles.

I think Spotify actually employs 'agents' that curate and search for new music for a given style or scene. I think Apple does too.

I very rarely search on Spotify. I've never created my own playlist.

If it's relevant, I would consider myself well versed in music. I studied it during my younger years, and whilst I don't these days - it's a passionate hobby of mine.

I just wanted to mention this, as you've mentioned things you want to do, that Spotify already does well, in my opinion. I can't speak for the other services.

That being said, maybe you could do it better. So I don't mean to discourage you.

If you could build something exactly like Spotify, that allows me to filter out songs with explicit content I would snap that up in a heartbeat. LOL.