Your MP3 should be fine.
If you want to access more data about your mp3 file, rather than just play, you will need a policy file that allows it. Similar to loading an image, if you just add it to the display it and don't access the pixels, it's all good, but if you want to access the pixels you should have permission(a crossdomain xml).
For images, when you call the load image, you can pass a LoaderContext in which you explicitly say you want to check for a crossdomain.xml file and get access to the content.
Similarly you should create a SoundLoaderContext with the second parameter set to true(to check) and use that in the sound load call.
e.g.
var snd:Sound = new Sound();
var req:URLRequest = new URLRequest("yourSound.mp3");
var context:SoundLoaderContext = new SoundLoaderContext(0, true);
snd.load(req, context);
snd.play();
For ID3 data you should listen for the ID3 event:
sound.addEventListener(Event.ID3, onID3);
function onID3(event:Event) {
for(var i in sound.id3)
trace('prop: ' + i + ' value: ' + sound.id3[i]);
}
For more info, you might find the mp3infoutil library handy.
HTH,
George