uhm... So you are going to put in the BEST AUDIO SYSTEM IN THE WORLD?
I'd suggest you get a decent Eclipse headunit with the features you need first off lots of outputs to hook amplifiers up to. Then, buy a set of component speakers from Image Dynamics that will fit, (the horns sound sooooo good) and a quality amplifier from PPI or JL or other to run them.
Next, get a subwoofer (s) that suits your space requirements. SS rl-p's from Soundsplinter, Jl Audio W6's, Image Dynamics IDQ's or IDmax's, Adire Bhramas, Shivas... Elemental Designs makes some great subs. Power them with a quality amp again by PPI, JL, Autotek, Elemental Designs...
Give us as much information as you can about waht you want to do to your car.