Most amp kits are fine. Most of them cheap out on the fuse holder. Make sure its not damaged when you get it (been there)

Strut tower apparently works well for a ground location.

LOC's will work fine, just use the factory rear speaker wires and tap them basically in the trunk.

Pull the power from the fuse box, down behind the P/S pump, through the grommet in the firewall, along the passenger side and into the trunk.

The easiest way to wire that is start from the trunk and go forward. Pull up the carpet on the passengers side and you should see a rubber grommet with the factory wiring harness going through it. pull it out then take a screwdriver and punch a hole in the rubber boot thats further in there. then push the wire down then fish it up.

Whip out the DMM and find a wire that has power (+12 DCV) in the trunk whenever the vehicle is on and off when the ignition is off.

Do you have onstar? Or had? If so, theres a pink wire in the connector that will work fine. You can either tap it or remove the onstar if you dont have a subscription.

No idea on the rear speakers for your car, only the older body style.

Do whatever you are willing to do. Components wont help you much if you're not willing to mount them properly.

Properly entails the tweeter on axis, the tweeter and midwoofer as close as possible, preferably within an inch of each other. (actual distance is based on the crossover frequency which i couldnt tell you since all speakers are different, even ones that are the same "model".

Run stock size unless you can fit larger. Never smaller. 6.5's fit in the sixth gens, no idea on the seventh.