One problem you may have towing something cutting brush is the sharp sticks left behind as they can pop atv tires (and tractor tires too) pretty quick. The old farmers trick was to use a dull bushhog blade. I typically do not cut a lot of woody debris so I have not had a problem with this (I chop down pastures of grass), it may or may not be a problem for you.
I was actually in your situation once when I had a broken tractor and wanted to knock down several acres of fields. I rented a walk-behind sickle bar mower, and liked the results, but had one issue. It was a lot of walking! That is a good thing health wise mostly, but when you rent a machine you need to get the most out of it in a short amount of time, so renting in that case was not the way to go. (Not that I am opposed to renting equipment, it just depends on the task at hand and what is being rented).
Believe it or not I am a huge fan of 2 wheel tractors (think BSC here). In fact I think a lot of smaller farms would benefit more from a 2 wheel tractor for $4000 then a $14,000 tractor that is extremely over-kill for a few acres. But don't despair on that $4000. A lot of times you can buy used 2 wheel tractors really cheaply, and even if not advertised, ask a rental shop if they would sell theirs. Most rental shops will sell anything as they can buy new and quickly recoup their costs. If you are crafty, you can adopt many items to operate by 2 wheel tractor. And if you decide even owning a 2 wheel tractor where you can start and stop at whim due to all the walking, you can buy/fabricate a small sulky that you sit on.
About the biggest drawback to a 2 wheel tractor is that they lack a loader. However I saw a unique wheel barrow that had forks on the front that used the leverage of the handles to move such things as pails, root balled trees and rocks. I always thought a person could do the same for a 2 wheel tractor, not having to lift, and yet having the load powered by wheels anywhere they wanted to go. In this way it would be more handy then a tractor that could not maneuver so easily.
However if budget is not even there for that, or you want to put it on a wish list down the road, you could fabricate a pull-behind batwing mower for your ATV really cheaply. All it takes is a rear end with tires, some pulleys and bearings. (skip ahead to about 7 minutes)
