I currently own a 2000 Chevrolet Cavalier that I am currently building a subwoofer install in.

My complete and current installs:

New Kenwood KDC-BT378U radio with built-in speaker amp, All new door and deck speakers. (COMPLETE)

Big 3 Kit, Mechman 270 AMP Alternator, (1) Sundown ZV6 12" 2-OHM 2500W Subwoofer (wired to 1 OHM), One run of 1/0 gauge wire complete with fuse and capacitor), Fiberglass Subwoofer Box(Not sure what size yet, any help on this would be greatly appreciated)

Just wondering if all the above installs with be able to comfortably power a 3000 watt amplifier to run the subwoofer properly? I know Sundown Subwoofers are underrated, just not sure if I want to over-power by more than 500W, seems safer to me like that, unless I'm wrong? Never dealt with this much power before, max was 600 watts before this build.

Any other install recommendations? Bigger battery because it is stock? Better springs for the added weight in the rear? Box will be fiberglass but the subwoofer alone weighs 95 pounds.

Thanks in advance guys.

First off, welcome to SSA.  Current supply wise, you should be pretty good, but hard to know for sure until installed and watching the voltage during music.

I can't comment on box size as I don't have experience with that sub, their site should have best info.

Battery upgrade will help for sure.  Maybe consider some deadening.