Does this come with the bolts and pins?

The hinge assembly itself is included. Fasteners and pivot pins are not confirmed in this listing — check your service manual for the exact bolt specs and any OEM hardware you may need to source separately.

Will this work if I only replace one side?

Yes. You can replace just the passenger side hinge. Your hood will function normally with a single-side replacement, though if both hinges are worn, replacing them as a pair will give you the smoothest operation.

How do I know if my hood hinge is actually bad?

Look for hood sag on one side, difficulty keeping the hood propped open without a prop rod, creaking when you open or close the hood, or gaps between the hood and fender that aren't even side-to-side. Any of those means hinge replacement will help.