Im not sure if any factory stereos come with any pre amp outputs? I guess take it out and check or see if you can find the specs for it somewhere...I dont really know how to install speakers with a factory amp, Any help here?
Where to you plan on mounting the amp? the trunk?
And as for speaker wire if the amps in the trunk you are going to need to run it to each front speaker so that will probably need to be around 15-18 feet each. Then just estimate how much you will need for the rears. (Not sure where your rears are)