Most users on this site, including myself, are not lawyers, so we are not able to give you legal advice. The best way to be sure is to consult a lawyer.
From the system you describe, it sounds like an artist or someone with the distribution rights to a song could claim that you are making unauthorized use of their identity/intellectual property, just for using the name of the artist & song. They might be able to claim you are using this property commercially (ie. you expect to attract more players, and more ad views, by using artists' names & song titles in shared maps than you would if the maps were based solely on your own IP).
Whether or not these claims would hold up in court is hard to say. Just keep in mind that you can be legally in the right and still be unable to afford defending against a lawsuit in court.
I think there's enough cause for concern here that you should definitely consult a lawyer before proceeding.