Hello from Somerset UK
Hi, Not sure if I can offer a great deal of help as am still learning, Slowly installing Audio, Nav and Bluetooth upgrades and Stuck with Sat Nav, hense joing forum.
I drive a 2004 E46 325 CI M Sport Convertible. Have managed to install a 10" Kenwood sub into the ski hatch, Kenwood Headunit, BT200 Unit, TMC Unit and DVD Nav. (Although Nav not giving guidance yet, please see Speed Sensor Wire thread)
For the future, may get the Leather re Trimmed and try to install Monitors in the back. (Need to hide that one from the wife for now though)
See you around.