When you go with aftermarket Head unit, you won't be able to use the factory bluetooth. You will need to get a add-on to a Head unit like the pioneers.
has some good Nav Headunits that use tomtom GPS. I like the Pioneer head units but im not the biggest fan of the Nav part of the system.
Also, the You do not have a standard size for radios. For instance 1DIN or 2 DIN. You will need to mod the sub dash.
you will also lose the factory DVD. At the most, you might be able to watch the movies still... but you will have to use the headphones. Modifications to your vehicle's sub-dash are required.
If the factory radio is replaced, the factory AUX input connection and factory SIRIUS action.
I have a REC for a 2006. I'm probably going to get a DVD receiver from pioneer this year or next and just get a garmin and keep it near by. You can set up the pioneer with a mic that you can hide in the dash or HUD.