Will this work with an aftermarket front bumper cover?

This bar mounts at the factory reinforcement points. If your aftermarket bumper uses the same mounting location, you're good. If it doesn't, test-fit before committing to installation.

Do I need to remove the OEM bumper to install this?

Yes. You'll need to disconnect the original bumper assembly to access the mounting points and swap in the reinforcement bar.

Should I paint this before or after installation?

Either works. Some builders prefer to paint off-vehicle for cleaner coverage. If you install first, mask and paint in place. The bar accepts standard automotive primers and topcoats.