stereo questions: Audio gurus, plz read!

[R3DL3TR5]

I have a '97 a4 with the bose stereo set up. I went to an upper-end audio store and was starting to look into stereo set-ups for my car. They told me that i have 5 1/4 components up front, 5 1/4 coaxials in the rear door, and 6.5's on the rear deck. All these are run through the stock amp. I don't know if all these sizes are right, do are they? Also, I'm looking at running a complete system...I was looking at doing this: (GURUS READ THIS!)-Diamond Audio s500s comps up front. And leave the rear doors stock and wired to the deck (Alpine CDA-9835). The rear deck would have the Diamond Audio coaxials. The speakers would all run on a Diamond D5 300.4 (4 channel) and then i have a 12" JL W6 that would be amped separately on a D3 600.1 (mono). Now, I'm trying to decide if i should replace the rear door speakers too, and if so, amp them? or....hmm, lots of different options. Also, with the headunit, I really wnat something with a semi-subtle look so that it doesn't conflict with my interior. I'm also really wanting to try to keep the display RED so it will match my dash lights. This alpine is really the only deck i could find to do that...Does anyone know of any others? lastly, are these amps/speakers sufficient? Will they accomidate each other well? Any and All suggestions or comments are welcome! Thanks a lot guys!
-wes m.

[Zodiak]

the guys at the audio shop were close. The fronts are actually 4" components with a .75" tweeter. But you can easily fit 5.25s and a 1" tweeter.

As far as leaving the rear door speakers alone and wired that's completely up to you. Rear speakers are really just there for the rear passengers and maybe a little rear fill, but if you turn off all your front speakers and just listen to the rear speakers, you'll see how little output they really have. I'm ditching all the stock speakers and the stock amp. As for the headunit. IIRC HarmonKardon make a very clean red backlit headunit (not flashy like most H/Us these days, more like our stock H/U)

[R3DL3TR5]

Thanks so much man for the help. What are your suggestions on where to find such a headunit? I think that online is really my only option. Thanks!
-wes m.