I bought a used tractor last May (New Holland TN65), about 8 months into owning our property. I can attest to the guy thing as i go around looking for things to use the tractor. I definitely recommend going with a 40-50 hp if you have 30 acres, and while recommending, i recommend 4wd. It is hard to describe all the reasons ---obviously it doesn't get stuck as easily, but the confidence you will have due to the increased surefooted-ness is amazing. Also if you get a front end loader, and i recommend that too, 4wd is almost a must, since the front end weight takes traction from the rear wheels. A FEL does the obvious, but it is a great mobile crane that transports heavy things as well. A tractor is another thing that, on the farm, is as handy as a pocket on a shirt.
With our hills, 4WD is mandatory. I've got a couple of hills that I could mow pretty effectively with a good bush hog and the willingness to back up the things for every pass. My neighbor does that on his 30 horse Kubota and, while it takes a little bit of time, he mows every bit of his property. It would be impossible without 4WD.
Plus, I'm not sure there's a good reason to own a tractor if you don't have a FEL!