Mixing Gnome and KDE apps is necessary and trouble-free. Quite often I like one app and not the other, for instance Kate and Gedit. But you can have both side-by-side on the same system. The Unity interface is, er, controversial, so in the lovely way of Linux, its now easy to turn it off and go back to the older style. Since I prefer my Linux-environment to be much of a developer fashion, I still am deviated more towards Gnome than KDE. As a novice user, I would have found KDE better if I had seen it, but since the time I first installed RHEL 4 on my desktop back in 2006, I opted for Gnome and loved it.
So, my recommendation would be to try them side-by-side, if you can compromise on storage, and see yourself. There has been much debates on which is better DE, but only end-user can check the pros and cons himself. Music is one of the “core” apps being built in GNOME 3. The idea is to have a set of basic tools to handle your documents, media, and networking needs. So far we have Files, Documents, Notes, Contacts, Music, Videos, Photos, Web… you get the idea. The apps are in different stages of maturity, but eventually the benefit of using the native GNOME apps instead of.