Well pl;an for a tad mroe than youd want cause once you get WiFi up and running along with a radio, mp3 CD DVD type shit you will want to do hot shit with it cause you can.
My buddies is set to just war drive as he goes along. So he can pull up Google maps and it tracks him and show it on the maps. While thats going on hes ripping you tube video and thats how he jams out. Plays the Music vids from youtube. I mean sure half of that is the "Why would i do that in my car or while driving" type shit but lets face it you do a carputer cause its cool. I think it'd be sorta cool to be able to watch yoursefl fly down the road on goole maps, jam videos from the Net and then let your passenger check their mail or IM all at the same time.
Not sure how much the devices pull but I dont think my boy needed that big of a PSU and hes got like all of it, HD radio jammer with teh GPS and all that horseshit.