As for budget, as little as we can get away with. There is a ton of other stuff that screams out for money as well. If paying cash $10K for the tractor with FEL and would be looking to get used attachments wherever we can. I'm seeing a huge price difference between that green or orange colored hardware and the generic brands that I see at the implement or farm supply stores.
As you ponder the decision between new and used, top tier and "generic" brands, keep well in mind the old mantra "The bitter taste of poor quality lingers long after the sweet taste of low price is forgotten."
Right now you have many great 0% finance options from major manufacturers that might allow you to get a new machine in great shape without draining your savings account right now.
You may well be better off with a 500 hour Kubota (for instance) than a random unsupported brand. If you are going to rely on the tractor, ensure that you have good service and parts support.
There is a huge difference between Kubota, Deere, Mahindra, LS, Kioti, and the random Chinese tractor sitting on a farm store lot.
Whatever you do, go out and test drive a bunch of tractors, both new and used, and get a feel for what your budget can buy you. It is also difficult if not impossible to get an idea of what the numerous frame/size classes of tractors equate to on the ground if you haven't driven them.
HP needs can easily be overestimated. I think for most people, a small horsepower deficit can be overcome simply with a slightly slower ground speed. Figure out how often you will be doing things that truly depend on overall horsepower- brush hogging (PTO), maybe. Pulling a drag harrow and most of your other stated uses can easily be done with a 20hp tractor.
Whatever you do, don't underestimate the usefulness of a front end loader and 4wd.