Fortunately I have enough MP3s from SoundCloud, Bandcamp and Internet Archive (incl. album art), but also from my CDs (ripped with Goldwave & Franzis Audio CD Ripper). And I have our own music (Frank's and mine) also as WAV on my Workstation PC, in case I will work with them and create remixes.
The German SHOUTcast Radio Broadcasters have to pay very much to the GEMA monthly, also if they play only Creative Commons Music and never GEMA-Music. I don't know, if other SHOUTcast Radio Broadcasters in other countries have more luck. I myself don't brodcast via SHOUTcast, I am broadcasting on Mixlr, and I don't have to pay to the GEMA.
This is a short guide, how Mixlr and Stereomix work:
http://www.lastfm.de/user/SabineKlar..._and_stereomix
Sure, You can push also music from YouTube through the Mixlr-App with Stereomix as Input, but SoundCloud has so many beautiful podcasts, mixes and also shorter tracks, and I can enqueue up to 24 hours SoundCloud-Tracks. Mostly I play via the SoundCloud-API...