Can I paint these, or do they come ready to use?

They're pre-primed and can be used as-is for a flat black finish. If you want color-matched covers, sand lightly with fine-grit paper and apply your base coat and clear over the primer.

Do I need fasteners to install these?

Installation hardware is not included with this set. You'll need fasteners compatible with factory door handle mounting points—check your service manual or test-fit first to confirm what you need.

Will these fit without removing the door panels?

These bolt to factory mounting points on the door handles themselves, so panel removal shouldn't be necessary for a straightforward swap.