Re: Standard Stereo Replacement....
There are some really good headunits out at the moment, and with great capabilitys of usb, mp3 (cd), and changer controls.
The only problem you will have is with the Original changer you have in the car which should be alpine??, if it is then the standard plug at the changer end changes into a oversize iso plug at the back of the headunit. If you went for a Alpine unit with Changer control you could then just run a new Bus cable through the car and then your changer will still work, hopefully if you get a good model eg CDA 9831, you will have mp3 capabilities.
I dont think your going to be able to have all of your requirments you list. If i were you go for a DAB system eg Sony or Blaupunkt, which has mp3 capabilities then you will have no need for a changer.