Here are my thoughts.
My acreage is wide open. No trees to maneuver. I even am considering a large 3 point attachment mower 10 ft wide or so, but I know that requires a larger tractor. I do not have the space to store (indoors) a large utility style, high HP farm tractor. Plus, I do not want such a heavy tractor to tear up the yard.
Tractors excell in wide open areas. It takes much longer for them to turn around so your lawn sounds like a good candidate. They also do better in square shaped areas as odd shaped lawns require more turn arounds.
The mowing area is not smooth, so mowing wide open throttle on the zero turn is not an option. So, the benefit of the zero turn being faster is not really a reality.
You will save time on a zeroturn when turning around. Tractors take significantly much more time to turn around at the end of the path. This requires a larger deck compared to the zeroturn to offset the time. Going from a 61" zeroturn to a 72" tractor will most likely result in increased time, especially if the area being mowed is not square. Not sure how hilly the ground is but a tractor will be more tippy side to side than a zeroturn, unless you put spacers on the wheel to make them sit wider.
The Kubota LX4020 is 32 pto hp. It should be able to handle a larger mower, I would step up to an 7' mower like the Woods TKP84.40, or Landpride FDR2584 or an 8' Woods RD990, or FDR3690. If your ground is level you could look at a tiny batwing finish mower, you would be on the low end of the horsepower range like the Woods TBW12.20 or Landpride AFM4211. If you have steep contours then a mounted 7' or 8' mower would be a better choice. I have mowed flat ground with a New Holland 3940 (45 pto hp) and a 16' finish batwing without an issue at 2.8 hp per foot. A Kubota LX4020 with a 11' finish mower is 2.9 hp per foot.
Depending on your soil types a tractor will have higher ground pressure than a zeroturn, this makes them more prone to rutting up the lawn, or creating areas with compaction. This reduces the days available to mow without tearing up the lawn. Also when turning the front wheel will dig in and tear the sod if the operator is not carefull and the mark is much large than the zero turn divit.
Tractors are not as easy to trim with A mid mount mower lets you trim on the side of the deck, a rear mount lets you back under trees or over banks, a batwing sucks at trimming. A zeroturn does much better at trimming off the side of the deck, and you can ddrive under trees with the front or hang a wheel over banks.
I plow with an ATV with 54" snowplow (Suzuki King Quad 500).
I do not know were you are in OH. Tractors will outperform an ATV in pushing power. The problem is that the blade is harder to float on gravel drives as you have no suspension to hold some of the blades weight like you do with an ATV. If your in the snow belt the ability to push much deeper snow than an ATV is a significant advantage. I find tractors to be much more controllable than an ATV when plowing. I plowed our drive for years with a Sportsman 500 and the high reverse speed was no fun, nor was struggling to push the handlebars at low speeds. I have plowed commercially with compact tractors and Kubota RTV's and found the tractors give you the best control for close in detail work. For pushing snow a tractor wins in my opinion. If your in the snow belt, or in the north west side of the state a blower is nice to have. Three point blowers have their disadvantages, but they work well.
My driveway is 450 ft of gravel, so maintenance is periodically required. I have no way to perform the maintenance now and either have to borrow or rent equipment to do it. Or pay a contractor. It seems like a front end loader and box blade combination would be great to have.
A loader will let you spread gravel, and do spot repairs with ease. However I would suggest a landscape plane/grading scraper might be a better choice for driveway maintenance. They are easier to learn to use compared to a box blade.
Being exposed to the elements is not exactly fun. My allergies are bad during mowing season and getting cold and wet during the plowing season is getting old quick.
I have terrible allergies, to the point were the lining of my nose is damaged so I cannot smell well so you have my sympathy. I love cabs and my next tractor will probably have one. A few things about cabs, Kubota cab tops are thin, almost a milk jug material, they do not like trees and one mating session with a tree limb and your out $1k. They make the machine top heavy so side to side stability on hills is compromised. I have not driven a LX with a cab, but had a coworker tip a Kubota BX with a cab just from turning to sharp at speed (I put it on two wheels turning it on a road). Compact tractor radiators clog easily and cleaning them out negates the advantage of a cab. Depends on what your doing but hot dry mowing can clog a radiator quickly. Blowing them out creates a dust bowl with you standing in the middle. Even using 36" wands does not solve the problem. So a cab is not perfect for allergies, but it is sure nice to not be in agony for hours.
Has anyone went from multiple, job specific machines to a tractor that can do it all? Any regrets?
I love a tractor for plowing snow with. However they are not that fun to mow with, as it takes longer and they are not as good at trimming. For my odd shaped lawns I would hate to mow them with a tractor. However having a cab might compensate for that. I cannot say that a tractor is a clear win, as I do not know what your snow removal or lawn looks like and there is also personal preference.