its better to get a head unit first, that way if you need motivation for getting new speakers you can turn up your new headunit til the stock 8watt speakers blow. the way i did it was subs & amp, head unit, 6x9's, front components. its better to get a headunit first though so you dont have to buy an adapter for the sub output for when you get subs and amp(s) not to mention the the enhanced clarity you will get from whatever speakers you are running inside the car. i ran the stock components in my gen4 for a while before i upgraded to boston acoustics. the stock sound is ok but when you compare it to any quality aftermarket brand you'll realize what you were missing. copy and paste the link in my sig to see my sound.
(also, how do i turn that address into a link on the sig itself?)