Do I need to mount a winch before installing this bumper?

No — the bumper installs first, then your winch plate bolts to the reinforced mounting tabs. Install the bumper, then add your winch kit separately.

Will this require any frame or mounting bracket modifications?

It mounts at factory attachment points with no drilling or welding needed. If your truck has the OEM brackets intact, this bolts on clean.

Does the matte black finish need primer or paint before install?

The finish ships ready to install as-is. If you want to match your truck's paint or add a protective clear coat, that's up to you — but it's not required out of the box.