Do I need fasteners to install this, or does it come with hardware?

Hardware is not included with this valance. You'll use your vehicle's factory mounting bolts, so check your service manual or hardware kit for the correct count and size before installation.

Can I install this myself with basic tools?

Yes. This bolts to factory mounting points — you'll need a socket set and a jack or lift to access the rear underbody. Plan for a couple hours if you're doing it for the first time.

Should I paint this before or after I bolt it on?

Either works. Some builders paint off-vehicle for easier masking. Others install first, then wet-sand and blend. If you go on-vehicle, mask your bumper cover and lights carefully.