Does this need a bulb, or does it come with one?

The assembly itself is included. Bulb specification and whether one is pre-installed are not confirmed — check your existing tail light bulb type or consult your owner's manual to ensure compatibility when you install.

Will this bolt straight up, or do I need to modify anything?

This assembly mounts at factory points with no drilling or cutting. Line up the assembly with your existing mounting holes and secure per your vehicle's setup.

Can I paint or seal this before installation?

The lens is hard panel construction. If you plan to paint, test a small area first to confirm adhesion. Seal any gaps between the assembly and body panel with weatherstripping or sealant to prevent water intrusion after install.