Do I need both left and right markers, or can I buy just one?

This is the left side only. If you need to replace both sides, order a second unit for the right marker.

Will this bolt directly onto my vehicle without any adapters?

This is a direct OEM replacement for the factory marker position. Refer to your owner's manual or dealer service guide for mounting point specifics.

Does the bulb come installed?

The housing is new and ready. Verify your bulb type with your service manual before installation — replacement bulbs are available separately if needed.