well, first thing i'd say to the guy selling it to you is that you want to custom order it. ES is a V6 right? i'm not sure, i have a 04 DE...anyways...
Audio:
you don't want the infinity system because you'll be installing your own. so you'll want the lower end faceplace and head unit...possibly ask for the 6 cd changer. the galant has a huge trunk so a custom box is the way to go. also, from experience, before or when you install the new system, get a new battery - either the yellow top or blue top (don't know the name) but it has 4 poles on it so you can connect more cables to it, 2 to your car and 2 to audio/whatever. if you don't - like i said experience - your thump will be delayed, a lot more when you're car is off, but you will still be able to tell when it's on. and when you do thump, those 3 plastic child seat anchor caps in the back under the window - you're going to want to pull them slightly up from their "secured/flush" position because they rattle.
the Screen you want to put in:
if you are going to go pay lots of money for a navigation/dvd head unit, then don't opt for the navigation package with the screen on top of the dash. but if you want to get real custom you can ask for the dash piece on top without the navigation package - install a CarPC with a touchscreen in that dash piece, computer under your seat or in the trunk, blahdy blahdy...thats a lot more to say,
mp3car.com build it to be cheaper, or buy the whole kit. or no dash piece and install it in place of the stock head unit and changer...it places it lower in the car (since a carPC technically isn't legal because it lets you do WHATEVER you want while you drive).
Rims:
personnaly, i don't think any car should have rims smaller than 18", i have 18's because i didn't want to spend more money on larger...you may be different. i have 18's and low-pros and my 9g looks like it's begging to be lowered because you can see a LOT of wheel well. i didn't even change the hight of my car by the rims because the upping in size and lowering in tire size were the same. if you get larger than 18 you probly won't need to lower it to look right. but lowering it is part of the fun! so i'd go 18 with lowering springs - WORKS, RRE, RPW, RIPP i think have springs...i know WORKS does. DO NOT BUY SPRINT lowering springs from ebay...they coil and are just crap.
HID headlights:
helios conversion kit 9007 if you don't have the projector lights, i forget the code if you do. pick the # thousand candle power you want that creates the color you want.
oui....ok just go to
club9g.com if you have any other interests/questions