Nissan 370Z Forum - Stereo Help

Could use some help with the planning of my audio system in my '10 Convert. Right now, I've got four 6" Kickers that I'm going to install (2 behind the seats firing up and 2 in the doors). I'd like to do something like jtgarza did
Nissan 370Z Forum - jtgarza3's Album: JL Fiberglass Sound System - Picture Nissan 370Z Forum - jtgarza3's Album: JL Fiberglass Sound System - Picture, but with the 2 extra Kickers in it.

That would mean that I need to get a 8" sub to put in the box between the seats and an amp to run it. I also need a great HU and maybe some tweeters. I've been looking at the Pioneer that Armhunter got, the new Alpine, or maybe a Kenwood.

Here is my requirements:
Head Unit-Love the thought of running Pandora and using a hard drive of some sort. It's gotta have a good nav and good user interface.
Sub-I listen mostly to rock and country, nothing too heavy, so it doesn't have to hit hard, just sound clear and sharp.
Amp-Do I need one to push the four speakers and one to push the sub or just one for all or none for the speakers and just one for the sub?
Tweeter-Should I replace the tweeter? The Kickers have tweets in them, so I don't know.

If you can't tell already, I know enough about car stereos just to get me in trouble. I would love to hear any suggestions so that I can start getting this together. I was looking at Wicked CAS or Crutchfield, any suggestions on either?

Thank you all for the help.