Depending on the speakers you put in you can usually get away with running the power from the deck for speaker power unless you want it really loud. We used all stock size speakers otherwise you will have fitment issues. I don't remember the gauge just look online and usually you can find what size you need. Check what power the speakers are and how much you plan on giving them. and there is actually 6 speakers in these cars. 2 in front(one in each door) and 4 in the rear (2 per side up by window) if your gonna run amp get a good 4 channel for the speakers. And run the rear sets together. Just join each side together. So 4 inputs just like normal only with 2 speakers wired together per side at the rear.
Here is a chart I pulled off the Internet for speaker wire. If my memory serves me correctly I think we used 14awg
Wire Size 2 ohm load 4 ohm load 6 ohm load 8 ohm load
22 AWG 3 feet max. 6 feet max 9 feet max 12 feet max
20 AWG 5 feet max 10 feet max. 15 feet max. 20 feet max
18 AWG 8 feet max 15 feet max 23 feet max 30 feet max
16 AWG 12 feet max 25 feet max 37 feet max 50 feet max
14 AWG 20 feet max 40 feet max ******* *******
12 AWG 31 feet max ******* ******* *******
10 AWG 50 feet max ******* ******* *******
