Welcome to TBN!
Looking for used, and in a lower price range, I would not immediately rule out any particular brand. As you learn more, and start to focus on the size and features you need, you can get a better idea which models would come close to fitting your needs, expectations and budget. You will also learn which brands are more "mainstream" and which are more risky purchases. A big indicator here is the dealer (and parts) support available within 50+/- miles of where you live.
You need a loader. Don't even consider buying a tractor without one. It's a costly proposition to buy a new loader for an old tractor.
Can you do without 4 wheel drive? Maybe. Is it nice to have for most situations? Yes.
You will get a lot of advice about the size of tractor you should buy. My interpretation of your post is that you should be looking in the medium to larger range of the "compact" category, and should avoid the subcompacts.
In the current John Deere lines, I would look for at least a 3000 series, or even a 4000 series. (Be careful - the older model designations for John Deere include a wide range of sizes as 4xxx models). In the Kubotas, I would look at the "L" models, and not at the "B" models or "BX" models. If you familiarize with these two brands, you have a basis of comparison with others, such as Massey Ferguson, New Holland, Case/IH, Kioti, Bobcat, etc.
With regard to horsepower, I wouldn't recommend anything less than 30. That said, lots of guys are happy with smaller tractors with less than that.
Visit some dealers and look at tractors to get an idea what size makes sense to you. After you've done a bit of research, ask to test-drive a few. Don't fall for the first thing you try. Try to get the feel of several before making a choice.
Good luck in your search!