As far as where you get the music from, you’ll have to determine for yourself what audio quality you require.
To test this, use something like Soulseek to get a high quality version of a song you are very familiar with, and then get the same song off of YouTube with yt-dlp (better yet—do this for a few songs). Then, open both songs in separate media player windows, randomize the layout of said windows so you don’t remember which is which, plug in your favorite headphones and see if you can guess which is which.
For me, I found the difference between a lossless or 320kbps download from Soulseek and a 128-196kbps download from YouTube to be negligible (or outright nonexistent) in most cases, so I mostly download off of YouTube, which is very simple to do.
Depending on where you get the files, you may need to add metadata yourself. For this, I recommend MusicBrainz Picard.