I have about double the acreage you have now (might wind up being up to 50 eventually), and simply couldn't get by without a tractor (have two now, and looking at a third to be dedicated to mowing). I started out with a used tractor to get my feet wet, and get a better idea of what I was going to need in a bigger, newer machine...that worked out well, but adds some time to the plan.
I don't think you'd want to go down to something the size of the B-series Kubotas. L-series, minimum of 30hp is probably where you'd want to look for starters. A 5' or 6' brush hog would do nicely to keep everything cut short, and you need about 5 PTO HP per foot of brush cutter to run comfortably.
When I started looking at new machines, I tried to look at almost every brand, and quickly realized that there are a couple of brands that give you more performance for the dollar than the others. I'm not saying this to brag, but I'm fortunate to have a wife with a killer job, and I do okay too, so I could write a check for pretty much any tractor in the compact, or utility categories, and not feel too much pain. Still, I couldn't justify the higher costs from the bigger names when I compared features, and performance.
After all of that, I narrowed it down to LS and Kioti....by far, the two value leaders when you compare price, power, size, etc, etc. I wound up buying a 47hp LS for $21,500, and if I'd gone with the Kioti, it would have been a bit more. If you go look at most of the big brands you can't get a similar tractor for under $30K. For a weekend warrior, I think that's a pretty significant savings. If I was running a rental shop, or farming every day of the week, the difference might not be nearly as significant. From what I've seen, the quality and construction seems to be every bit as good, and I'm only missing out on minor frills like an eThrottle that adjusts itself when you step on the pedals...not a big deal. I'm just coming up on 100hrs (after 5 months), and all I've done is the 50hr service, and add diesel
The most important thing is to try as many tractors as possible....sit in them, run them a little bit, and see what you like, and don't like. Sometimes little things will become obvious that you didn't consider when looking at the specs. The good thing is that pretty much everybody makes good machines in this size class right now....lots of competition, so it's hard to go wrong. Good luck!