Technically you can do it either way with the big 3. It'll look cleaner if you replace the wires with 0 gauge and wrap it in loom. I usually don't feel bad about extra wires. I recently helped someone in a hurry and replaced a broken wire to body metal but added new ground wires from battery to block and block to frame, so everything meets back at the block closest to the alternator. He had serious voltage drop just from rolling windows down cuz his grounds were shit on a 05 avalanche. Now it stays pretty steady with a 2k amp and one yellow top.
There's a lot of amps that will fit your needs.
Personally I'd buy a cab 22. Bobby would buy a Taramps.
Taramps have come a long way with their "smart" stuff.
Spend some extra time researching the amps and the difference between Korean, Chinese, and Brazilian boards as well as half bridge vs full bridge.
Or just buy the thing and smile while the bass bumps