Bro, what u wanna do is get 3 subs. Jst get cheap ones cus 3 cheap ones are btter thn 1 good one. You wanna get 4 6x9s caus 4 is bettr.Then you wanna hook it all up to the one amp dont worry if they tell you its not enuf powr caus you wanna look at MAX powr, and get all poineer caus my mate has a full poineer setup and its sick, once ya got it all you wanna wire it up like dis-
you will need a head unit removal tool, to take the head-unit out. Go to Jaycar or somewhere similar to grab one. If you are putting a single DIN head-unit in, than you will need to get a pocket to mount beneath it, to fill the hole the standard POS came out of.
Do a search and someone will have covered the topic already in more detail.