personaly, i wouldnt even bother with the dash speakers and just focus on the doors, just find a decent pair of 6.5s and some sound deadener (or closed foam duct insulation from home depot) and line the inside of your doors behind the door pannel, and maybe put an amp on the 6.5s depending on how much wattage they want.
being that you are 15, im sure you dont have a lot to spend on subs, but some good subs can be had at a relatively low price.
look at some of the dayton subs on parts express
they are relatively inexpencive, have good specs and are very well made, and the Quatro is a very nice sound quality sub, as well as the Reference HF
for wire i suggest ebay or find a local welding store that has at least 4 awg and you will need about 20 feet.
as for amps, i would look around on ebay at the soundstorm cruisers, they arent the best amps in the world, but they will do what you need and should sound alright, if you want nicer amps look at sundown or us amps.