You're lucky because your battery is under the back seat (assuming it hasn't changed since 02). Keeps your power wire runs short and you don't need to go through the firewall.
You can probably just order an amp wiring kit. I'm sure 8 gauge would be fine for that amp. It never hurts to go bigger though (bigger wire = smaller number gauge). Put a fuse a few inches off the battery on the power wire. The fuse will come with your wiring kit. Ground the amp to bare metal on a bolt somewhere in the trunk. I grounded mine to a bolt on the shock mount and it was a good ground.
You'll need a new battery post to attach the wire to the GM side post battery. You can get them at auto parts stores.
Are you using an aftermarket HU? If so...
Remote turn on comes from the back of your headunit.
You'll need to run RCAs from your headunit to the amp.
You'll need some speaker wire to run from the amp to your crossovers, and from the crossover to your speakers. I used 14 gauge in my car, but that may have been overkill. I put my crossover in the trunk so I had 4 runs of speaker wire going to the front of the car (2 for woofers 2 for tweeters). Probably want to get a good amount. You don't need super expensive stuff. I used Scosche brand from Wal Mart. I think I used 2 rolls that were like $10 a piece.
I think I ran all the speaker wire down the driver'* side of the car. Run the wire through the rubber boot into the door and hook it up.
It'* pretty easy overall, just take your time. Look up some info on the web and get some ideas on how it works.
Don't forget to disconnect the neg. battery wire.