I would suggest an aftermarket head with Bluetooth. I prefer "double din" because it fills the entire space and gives a bigger display, but some prefer single din. A touch screen is also an option, but will cost more. A nice Pioneer unit is $140 at Sonic Electronix and comes with the mounting kit and wiring harness for your Aveo. I would install shallow mount 6 1/2s with a 1" spacer in the front doors. (I'm doing this myself this spring, as soon as time permits.) Here's a good write up: https://plus.google.com/photos/10102...er=pwa&sview=7
You could also go with components where you mount a 6 1/2 woofer in the door but there's also a tweeter to mount on the a pillar. Of course it costs more and if this is your first install, mounting tweeters and crossovers is a little more involved for the novice. For the rear you've got 4x6s, so your choices are somewhat limited. A new set of 4x6s would be simplest. Ive never looked too hard into what other speakers others have shoehorned in there, as I have a sedan, so I can't comment much further. And then if you want to add a sub that's something you could add at a later date.