First and foremost, your budget determines how much mower you purchase. If budget were of no concern, I'd stay away from the Cub 10XX series as they are lighter yard tractors. Same goes for the John Deere X300 series. I have a 54" LA175 John Deere that I use to cut approx. 3 acres of yard and NO brush hogging. It does a fine job, but I don't expect it to last forever. IMO, the X300's are just a slightly beefed up version of the 100's with some shared components, such as the transaxle. I've never owned one, but I've heard great things about the 2000 series Cubs. If you bleed green, then I'd suggest the X500 series. Much heavier tractor than the X300's.
As far as the brush hogging goes, it all depends on how far you let that area go between mowings. If you let it get waist high with small trees growing before you mow, then forget it. You'll need a rough cut mower for that. With that said, you can buy a pull-behind rough cut mower like a Swisher that will do that job for you. If you let it get up around a foot high with no hard woody growth, just field grass like fescue, then your tractor will do it. However, the lighter of a tractor you buy, it will take you longer to mow the field and you should expect maintenance/repairs sooner and more frequently due to the stresses of mowing tall/thick grass or weeds.
If budget is a big concern, you might want to look for a heavier used tractor. For instance, there is a 2005 John Deere X495 diesel with a 62" deck for sale locally. It looks nearly new, only has 245 hours on it and the guy wants $5,500. This is the last year the X495 was made, they went to the X700 series in 2006. I priced a new equivalent on the JD website and it was right at $12k. If you have some time to shop around, keep your eyes open for a nice used tractor.