Those base coats have a hardener that goes in them, but most people do not use them.
Will toughen up the base coat considerably. You can sand with 600 to 1000 grit. If it's chipped sand out like skid lid suggested and feather it out well or you will see a ring around the repair area after cleared. I'm assuming black so it shows everything. Just take your time. Even 8f the clear doesn't look great or have lots of trash put a few coats of clear and you can sand buff anything to make it look fantastic. Good luck. Posts some pics of the finished project.