You need to break down the project in terms of all libraries you'll need. So, GUI, playing music from files, accessing the file system, playing music from a stream and so on. For the GUI part, if you wanna make it as customizable as foobar's, you wanna make sure the library you use allows for that level of control over its GUI elements. Basically, just think of all the basic elements of the program and try to find some libraries that implement each individual piece. Use whatever language you feel more comfortable with that also has those libraries. And just start researching and trying things out.
You need to break down the project in terms of all libraries you'll need. So, GUI, playing music from files, accessing the file system, playing music from a stream and so on. For the GUI part, if you wanna make it as customizable as foobar's, you wanna make sure the library you use allows for that level of control over its GUI elements. Basically, just think of all the basic elements of the program and try to find some libraries that implement each individual piece. Use whatever language you feel more comfortable with that also has those libraries. And just start researching and trying things out.