I would be leary of busting brush if I didn't have a FEL on the tractor. As described, run the bucket down low as a "feeler" and move along at a slow speed. Even doing this, I tore out my rear light wiring on 2 occasions. It was kind of silly the way they ran it down alongside the transmission case so I have re-located it above the floor plates out of harms way. Also be aware of backing out of brush you have pushed your way into. All those branches, sapplings and bushes that have been pushed down with the loader will try and stand back up into the tractor works, steering and front axel so keep your eyes open. I had a piece of cedar escape my view and it found it's way up and into the alternator pully, straightining all the cooling fins on the pully and popping the belt off. With a slightly different path, it could have just as easilly found it's way to the back side of the cooling fan and radiator so beware.
I am not sure how large your tractor is but mine(28HP/2500#) easilly pushes over just about everything up to 4" and the 5' hog on the back shreds it all down nicely. I occasionally have to lift the mower to let it catch it's breath on the larger stuff and lower it down slowly to finish the shred. I don't especially like guards on the mower for working in the brush but I am also away from anything. If there is other property or people/livestock in the area, guards are a must as it WILL throw some pretty large stuff particularly while shredding sapplings and branches.
Because of terrain and the ammount of room I have to maneuver, I occasionally have to lead with the mower and back it into the brush. I have bent the 3PH mounting this way running into immoveable objects. I prefer to start with the deck up high, back it into the brush and lower it down slowly with my foot guarding the clutch and prepared to halt or raise the 3PH immediatly. Lowering it onto a stump or large rock can be pretty exciting
I have formed a few brushhog opinions over the years If you are in the market for a hog with plans on busting a lot of brush. Look for the one with the heaviest sidewalls/weight your 3PH will take. The sidewalls take a real beating when the shredded chunks of wood and occasional rock starts dancing around under the deck. If the sidewalls are thin, it won't look like a brushhog for long when busting brush. Make sure the sidewalls have skids. The skids welded along the bottom of the sidewalls will also help the sides keep their shape. There are some that look like they have "I" beams for sidewalls and that is good as if it is worked on rough terrain, the skids on the sidewalls will help to keep the blades up out of the dirt/rocks while passing over humps. A large "stump jumper"(disc that covers and protects spindle and blade carriers) is better than a smaller one. Also look for the deck lift linkage(the part of the lift framework that connects the rear of the deck up to the toplink) to be flexible. The mower I use has a piece of chain and flatstrap which allows the deck to tilt up as the tractor passes over dips and rises. If it dosn't have this, you will most likley bend that structure if opperating it over rough ground.
Good Luck and happy "busting"