I'd say buy an alpine mrv-345 or 545, and buy 2 sets of alpine-r coaxials or components, whichever you feel like installing (have to hide the crossovers in front doors which is a ***** unless you feel like running a ****load of wire).
Buy them off ebay from some reliable dealer. I got my 2 pairs of component for 250 shipped. The coaxials are cheaper, sound similar, just doesnt have the same sound stage, but that's not really noticeable unless you live car audio.
The amp would probably be ~150.
Install the amp using "9-wire" so you dont have to run wire through your door and bam. awesome sound.
Now, that's provided you want some badass speakers that SCREAM at full volume with awesome sound reproduction and very clear mids/highs.
I would highly recommend this setup as I have 5.25 comp in the front and 6.5 comp in the rear deck behind the seats, with the tweeters in the A and C pillars.
If your looking for a non amp setup, I would just say get the lowest model kicker available for your doors, as they are just a wee step up from stockers and will run off headunit power no prob and sound fine for low-moderate volume.
4" rear, 5.25 fronts.
If you want more information either way just pm me, I've run both setups (kicker first, then upgraded) and have so many hours of a completely stripped internal wrx it's almost too much.