I like your thinking about at least 50 hp at the pto, MFWD, and no cab. I was in a similar situation a long time ago and that did the trick for me. If I were you I wouldn't limit myself to a particular brand but rather look to see what becomes available on Craigslist and at local dealerships. Personally I'd restrict myself to a big brand tractor like Deere, Kubota, Case-IH, or New Holland, and watch for whatever turns up. Some of the other brands come and go, or at least the dealerships do, while somebody always wants a franchise from one of the big boys. I am also a big fan of weight whenever I purchase equipment. Yes a heavier tractor will leave bigger ruts, and no you can't mow your lawn without tearing things up some, but more weight gets more power on the ground. 140 acres isn't the place for a suburban homeowners dream tractor. I wouldn't consider any tires except Ag for your needs.
A utility size tractor should also provide you with a pretty good hydraulic flow rate which you will find useful at some point, look for a machine with some remote hydraulic outlets, they won't add much if anything to the cost and you'll thank yourself later.