My dad had polio and could not walk. I grew up on 24 acres, and he did a lot of mowing on the meadows there. He had Wheel Horse tractors from 5 to 18 HP, and then a GE ElectTrac.
All the tractors were modified by a local company, which interestingly enough was run by another gentleman that had polio and was wheel chair bound. That let him focus on good solutions. Translating that experience into something you can use today, I'd say that you want to find someone to modify tractors that has done it before.
This is the only picture I have of him on a tractor. You can see the straps added to keep his legs in. On the tractor's left, you can see a rod added that went down to the break pedal. On this tractor, as well as some of the others, the speed control was on the dash, much like my current JD 318. More and more, hydros use pedals. If you can get a tractor with electronic hydro control (Deere calls it "e-hydro") then it's a "plow by wire" tractor and the controls foot controls might be adaptable to something on the side of the dash.
Terrain will play a big role in what you do. How you keep your body "under control" when the tractor moves around is all part of the adaptation puzzle. Not sure what you mean by "being a quad", but if that means no arm control then the adaptation problem changes greatly. In your favor though, the world is geared up to adapt better than it was 50 years ago.
Only the 1st tractor we had was a gear, the rest were hydro. There is no doubt in my mind you want a hydrostatic transmission.
About age 65 it was to hard on his shoulders to swing himself up from the chair to the tractor. There were various solutions to this that were possible, such as a beam type lift or harness lift. I've always wondered how things might have been if he had adopted those tools earlier on. Would he have had more time because his shoulders didn't wear out as fast? Anyway, key concept here is work on some way to assist yourself getting on the tractor even if you can swing it now.
Finally, you have not mentioned other aspects of your life, so let me toss this out. I had a blast as a kid going around with my Dad doing things outdoors. It was a great match-up. When all us kids left home, the place was in pretty good shape and all he did was mow. So don't forget to factor in what sort of help you'll have. The right assistant for some jobs won't be a burden, and the experience can be good for all. Once the land is in good shape, you can mow alone and enjoy that experience.
Also, once my dad stopped using the tractor, he got a beefed up wheel chair that would still let him drive around the property. He paid others to cut the property. This was a nice way to transition out of driving a tractor. So keep the future in mind when working your land.
So by all means try to have someone adapt a tractor to your needs. Scale your needs so they are within your limits. Hopefully there are others who can accompany you on occasions as you tackle projects. And try to "terra form" your land so you can still enjoy it down the road when tractoring might not work. I don't know the specifics of your situation, but I assure know I know the determination you have.
Pete
