as far as the stereo goes I have learned alot since buying my car. I am planning on putting in the same radio youre talking about, however it will not fit in the opening where the original stereo fits now. What I am doing is Im going to order the dash piece for the 300c with navigation, that has plenty of room for the kenwood you want, and the piece is only about $140. Then you just swap dash pieces and take out the small storage compartment under the ac controls. Also if you install a different radio you have to have the system rewired because it cmes from the factory wired with data cable, so I was told its best to rewire (I dunno that may be a crock of shit) but my guy is really good, and this should take care of the small opening that we have.
The stock stereo is a Double DIN unit. An Aftermarket Double DIN unit or a Single DIN unit will mount fine in the stock Dash piece according to crutchfield. They are selling the faceplates with the kits and also selling an aftermarket wiring harness. The only 'rewiring' that needs to be done, is the Aftermarket head unit ACC lead wired to the fuse box or ignition. One of the drawbacks of having these faceplates installed, is that you still have the knob gaps on the side of the dash piece.
On the other hand, there is currently no adapter for the NAV based Dash piece. You will have to have one fabricated until one is released. Crutchfield said they are expecting this soon. This option will look closer to OEM if done correctly... The G-Unit 300c is setup this way. Stock NAV yanked and replaced with Aftermarket Alpine.
I take delivery of my 300c on saturday. I eventually plan on retrofitting a touch screen LCD to the NAV dash bezel so that I can setup a carputer complete with XM, FM, TV Tuner, DVD, Mp3, DIVX, Carpoint 7 Navigation, and whatever else the mind can think of. I'm thinking I can fit a 8" - 10" touchscreen LCD in there and make it look very OEM. Check out mp3car.com for more info.
If I eventually do get around to going this route, I may start selling the NAV Bezels complete with LCD touchscreens. Any interest in this?