The other idea would be to get all of the small trees and brush cut, then rent a chipper for the day and grind it up. To me that would be the best way to deal with it. As for the ground, the box blade will work, it will bring up tons and tons of roots though, so that will create a whole new problem. Running around with the brush hog is a great idea, just be careful of stumps and flying debris if you try an lower it on bigger brush. On rough land we have used a power rake which attaches to a tractor to level things out, I don't think there is an attachment that works as well.
Good luck
Adam
Good luck
Adam