I have read your thread and you bring up several different topics.
1. The compact tractor industry is mainly built around providing a machine for grounds maintenance for suburban properties and "hobby farms." If you think of the stereotypical "horse lady" who has a handful of horses on 10-15 acres and needs a little tractor to smooth the driveway, mow lawns and clip pastures, and help unload small square bales (that somebody else made) and landscaping materials from a trailer or pickup truck bed, that's the target market. That results in a fairly lightweight machine on tires that are designed to decrease turf damage, hydrostatic transmissions, to and nearly universally set up with a loader. PTO power is high for the weight as mowing is one of the main applications. Older farm tractors like the Ford 3000 were primarily designed to pull tillage equipment and are much heavier for their power levels than modern compact tractors. They nearly always came with regular gear transmissions, a few oddball IH and Ford units being the rare exceptions. They also nearly always came with ag tires, often fluid filled.
2. You can still get a tractor fairly similar to a Ford 3000 brand new. Note that a Ford 3000 is a much larger tractor than a 3 series John Deere, it's somewhere between a 4 and 5 series in size. A 2WD New Holland Workmaster 50 or its red clone has 6 more HP, is a few inches longer (the measurements in tractordata.com are very wrong) and a few hundred pounds more weight. Deere's 2WD 5045E is slightly larger than the Workmaster but in the same class and actually makes 50 HP and not 45. If you want something a little smaller than the Ford 3000 rather than a little larger, then a Kubota MX5400 2WD will be slightly smaller and a roughly 500 pounds lighter. All of these new tractors have 8 or 9 speed gear transmissions, 2WD, and are open station, and roughly similar size, weight, and power to the Ford 3000.
3. If you want to mow 20 acres of grass that's too rough to mow with a front deck mower or zero turn but you want it to look nicer than if you used a typical rotary cutter to knock it down a few times per year, you have a few options. One, you can continue to clean it up to where it is smooth enough you can use a front deck or zero turn mower and mow it like a giant 20 acre lawn. Or, you could get a big pull behind finish mower and mow it with a tractor. Two, you can use a finer cut flail mower behind a 40+ HP compact or small utility tractor (such as the units I listed above) on industrial or turf tires. Three, a rotary cutter actually does a pretty decent job of keeping things semi-finish mowed if the blades aren't completely trashed and you don't let things get 4' tall before you cut it. I use a rotary cutter to cut the ditches along my 1/3 mile gravel driveway every 3-4 weeks. The cut quality in doing that looks a lot better compared to the field right next to the driveway where I only cut it 3-4 times per year using the exact same cutter. This area is also a little too rough to want to use a finish mower to cut. It appears that this situation is in general what you are dealing with, so I would give that a shot with mowing once a month or so with a rotary cutter if I were you. A 5-6' one with a 30-40 HP tractor (such as one of the 3 series Deeres you mentioned above) would be reasonably sized for 20 acres without being too much of a bull in the china shop if you have anything to mow around. That would certainly be simpler than trying to import some unusual European tractor or getting a very niche machine here in the USA.
4. Regarding PTOs, you can get either a transmission driven PTO, a 2-stage live PTO, or an independent PTO. A transmission PTO has one clutch for both the transmission and the PTO, so when you step on the clutch, everything stops. Some Kubotas and the Deere 3D, as well as a bunch of old tractors have this setup. A 2-stage live PTO is seen on some Kubotas and a bunch of '60s-'80s tractors. Step on the clutch a little and the transmission stops but the PTO keeps turning, step down all of the way and then the PTO stops too. Most new tractors are independent PTO with a totally separate clutch for the PTO and transmission. You can either get an electrohydraulic PTO clutch with a little button you push to engage/disengage the PTO or a mechanical PTO clutch where you have a lever to engage/disengage the PTO. Independent PTOs are the most straightforward to operate but a live PTO can be fine too if you aren't too ham-fisted to mash down on the clutch all of the way all of the time. It would be a bit trickier to operate a transmission-driven PTO with using a PTO-powered implement, in general you don't want to have to stop, change gears, or reverse with the PTO engaged.