Back to the OP's question. You have difficult terrain which is going to call for a larger tractor. Try your brothers 4120 at your place for a week if you can and see how it is. If you can afford, buy one, or find one used. You can't go much below the 3520 and get away with it to share implements. The problem with the 3000 series is track width. They are a bit narrow as they come from the factory and many owners have widened them with 8lug skid steer spacers from Prowler on eBay. I have also purchased a set and will be adding 4" per side. The 2000 series is going to be too small for your terrain and property.
Honestly you should be looking at the 5045e. It's going to cost less than several of the compact tractors, it has weight, wheelbase, and track width which will work well on the hills. It is unfortunate that they used and e as the designation. They are more than just economy tractors, it's just that they don't have as many options. I think they are nicer than the NH Workmasters but that's another tractor you could look at. Also look at the Kioti DK45, DK50, and DK55 ( which may be EXACTLY what you are looking for at a price you can afford).