Will this lip interfere with my trunk seal or undercarriage when parked on a slope?

The lip extends minimally from the fascia plane. Before final installation, check ground clearance at your vehicle's typical ride height and on a slope. If ramps or driveways are steep in your area, test fit first to confirm adequate clearance.

Does this cut into the brake light area, or do I need to modify the tail lamp housing?

This is a front lip; it does not affect brake lights. Your rear lighting remains untouched. The front fascia should accommodate the lip without cutout work, but verify fit against your bumper's specific contours before adhesive or drilling.

Should I bond this with adhesive or drill through the bumper for fasteners?

FRP lips can be installed either way depending on your preference and bumper construction. Adhesive is cleaner and reversible; mechanical fastening is more permanent. Both require proper surface prep—sand and clean the mounting surfaces thoroughly. Your choice depends on whether you want the option to remove it later.