Will this fit with my stock cat?

Yes. This is a catback system — it bolts to the factory catalytic converter. Your stock cat stays in place and untouched.

Do I need to remove anything under the car before installation?

You'll need to drop the original exhaust system, which typically means removing heat shields and a few mounting bolts. No drilling or welding. Refer to your service manual for torque specs on reassembly.

Will the burnt tips stay that color?

Burnt finish will dull and discolor over time from heat and moisture. Expect patina buildup — it's part of the character. Light polishing restores shine if you want it.