it all really depends on the owner of the music you broadcast. They at the very least want to have sayso on whether you play it or not. This is where the DMCA gets involved. By paying the royalty fee passed recently you will have access to any musical recording under the US copyright office regardless of whether the owner allows it or not. Whether you generate revenue or not is really a non-issue in this case. because as the horse has been beat to death on the arguement of which party provides value, the DMCA has given the RIAA and other recording companies the green light to charge you because you gain a benefit from using their work. Which is in this case more popularity.
That only covers half of what you legally need to protect yourself. You also need to get a license for the written work. From BMI, ASCAP etc.
All of this above applies to US based broadcasting entities, if you live in another country, you probably have different rules.
To put this in perspective for you, not many non-revenue generating stations shut down because of licensing this year, because a) they don't care to pay b) they don't know they have to pay or c) they have worked out deals/wavers individually with the artists they broadcast.
How you proceed is up to you
Disclaimer: I am not a lawyer, I did not take the bar test, all you see above is based on my 3 years of experience in the streaming media community.