You've got a good tractor and a good cutter, but going after big brush can really take its toll.
The mower might handle it with a few dents in the side walls, but your tractor and your tires may not be quite as forgiving. Pushing fairly large brush over before running it under the brush hog can do a lot of nasty things to the underside of your tractor -- like puncturing your hydraulic filter, ripping hydraulic lines, and pulling wire harnesses apart.
When the mower cuts, it usually leaves a pretty nasty stub sticking out of the ground. When that stub dries, it can go right through a tire the next time you clear.
Pushing brush over for a rear mounted mower be pretty hard on your paint job too.
I'd suggest you either start with a good heavy duty brush cutter or a chain saw. One other good alternative is to get a tooth bar for your loader and go out after a good soaking rain. You might be surprised at how well your tractor will pull roots out with a tooth bar.
Good luck,
Knute