The wire size is going to depend on what you are running. Amps,lights,etc. Your stereo shop should be able to help you. You might want to run just a tad bigger incase your needs expand latter on you won't need to re-run the wire. However the heavier you make the wire the less flexiability you will have on how to run it since it won't bend well. In addition the extra wire will place additional resistance on the power going into it causeing less power to flow efficiently. But that should be of little concern in this circumstance.