The glove box USB is kind of a pain to find - luckily when they prepped my car, they left the tag attached so I could find it. It is in the upper left corner of the box, inside the lip. You are kind of going in blind. Once you find it, I suppose it would be best to just leave the USB plugged in so that you don't have to do the hunt and peck.
I found it easier to upload my playlists via the cable (I didn't get a cable with the car; maybe because I have iDrive???) but my standard Apple USB cable worked fine. Once uploaded I could control through iDrive system. Could also play through Bluetooth, but not specific playlists. If I didn't like a particular choice, I could use the steering wheel controls to switch songs.