I am with clemsonfor. What is your endstate? Are you trying to do any grading, or just want to clean up the trash/debris when you are finished cutting. If they are just small branches and weeds, just bushhog and let it shred the branches and weeds, and then let it lay to mulch. If the branches are large enough to require pushing out of the way, you will need to do that before you bushhog. Do you have a front end loader? If so, I would use that to pile up the brush - before or after doesn't make a difference.
Hawk