Do I need any fasteners or hardware to install this?

The handle uses factory mounting points, but hardware specifics aren't detailed in the listing — check your existing handle before removal to confirm what fasteners you'll need to transfer or source.

Will this work if my door panel is already off the vehicle?

Yes. The handle bolts directly to the door from the interior side. Having the door panel removed makes installation easier, but it's not required.

Can I use this handle as a key entry point, or is the keyhole just for show?

The keyhole is functional — it's designed to work with your existing key for door lock operation, just like the original.