Just based upon those photos, I would not be reluctant to brush hog them with a tractor, along as the caveats a few others provided are followed.
Dry conditions.
Wheels set at widest position and filled.
R1 ag tires
Up and down with no side-hill operations and turn around at top or bottom flat areas.
If FEL equipped, bucket kept low to ground as front balance/ballast going forward uphill. If no FEL, some front-end weights.
Those slopes do not look too steep to accomplish the brush clearance you mentioned. Walk the intended area first to check for potential problem areas.
Up and down hill is not too problematic as long as you go slow and carefully. As your experience level grows, you will develop more a a feel for what you are doing.
As far as the tractors selected, look at the intended growth and determine maximum stem/trunk diameter and match that to the rotary cutter, then let the cutter's HP requirements determine your tractor HP needs.
Also, as others have mentioned, HST and 4wd.