Please advise on parts.

[nebulight]

Okay, I'm not stupid when it comes to cars; I've built 3 400+whp cars so I know what I'm doing under the hood. I switched to a Yaris because my turbo Intergra was stolen, so now I'm going for gas milage instead of power (still can only best 37.4mpg, I guess it's my lead foot).

However, I have NO CLUE when it comes to car audio. I really don't like a lot of bass, but the little bass I do want, I want it to be clean. I really don't listen to it insanely loud, but I would like it loud enough to be clean on the highway. Basically, I want it to be really good quality. I do know that all my parts will be Kicker because I get most of the stuff for dirt cheap, and I mean DIRT cheap. I have a list of all the Kicker parts, and this is what a buddy of mine told me to get:

KS Series Coaxial Speakers KS 5 1/4" w/20mm tweeter (055KS525)
KS Series Coaxial Speakers KS 6 1/2" w/20mm tweeter (055KS60)
ZX Series Amp ZX400.1 400 Watts x 1 Amplifer (06ZX4001)
L5 Series Sub 10" Solobaris L5 Sub Box - Vented, Thin Profile (06TS10LS)
Pioneer AVIC Z1 (at some point, want to try to stick with the stock head unit first)

Now I'm not sure about coax speakers versus component speakers for what I want (see above). Would there be that much of a different to worry about where to mount the tweeters in the yaris? Also, more importantly, should I get a separate amp to power the speakers? So people tell me that I should, so are saying no I don't. Since I have no clue on what to do, I don't know what to believe. If I do get another amp just for the speakers, I was thinking about this one:

ZX Series Amp ZX350.4 90 Watts x 4 Amplifer (06ZX4001)

But then I saw this other amp, that will power the speakers and the sub in one unit (forgive my ignorance on the subject, this is all new to me):

ZX Series Amp ZX700.5 85 Watts x 4, 420 x 1 Amplifer (06ZX4001)

Do you lose anything when using one amp versus two? Also, wouldn't it make sense to get just one amp since the back of the liftback is so small, or could you mount it somewhere else?

Also, do you think the car would rattle with this setup? My liftback rattles enough as it is without even playing any music and it annoys me!