Will the front lip interfere with my trunk or rear bumper fitment?

No. This is a front-end component only. Rear clearance and trunk operation are unaffected. Verify your bumper mounting points are in stock condition before installation.

Should I use adhesive or drill through the bumper to mount this?

Both methods work depending on your bumper condition and preference. Adhesive bonding is cleaner for stock bumpers; drilling allows for bolt-through security if you're upgrading other front-end components simultaneously. Prep your mounting surface thoroughly regardless of method.

Does this stay stable at highway speed without additional bracing?

Yes. The two-piece design is engineered for bolt-on security. Ensure both panels are fully tightened before driving, and inspect mounting hardware periodically for any loosening due to road vibration.