Congratulations on the car. I love the W124 coupes. I can't answer most of your questions, but I do know that an Alpine (CHM-S620) is about the only changer that's compatible with the head unit. You'll also need an adapter (check the audio archives as there are several companies that make them). The phone in my '95 E320 was removed but I agree, the stock phone is light years out of date.