Ok lets cut to the basics here. We are talking about mowing 3.5 acres. Cost is a big consideration. If we want to eliminate all our favorites, and if we want to take this down to the basics, the we are not talking about a real tractor. A MURRAY or an MTD purchased at the local hardware store will mow 3.5 acres. Further, if he needs to haul things then a $99 cart can be towed by the above said lawn toy tractor and that is much cheaper than a FEL. Generally safety is not an issue with a lawn toy tractor because no ground engaging equipment is used so tipping is virtually not an issue.
However, if we want to get back to the post about some different equipment, I simply tried to lay out, without too much bias, each of his options from antique to grey market to various types of new tractors from various nations with various features.
Regarding ROPS on flat land. People should have ROPS on every tractor regardless of terrain if they ever use any ground engaging equipment. I can flip my 2 ton antique Oliver just as easily as I can flip my little NH TC24D if I drop the plow and turn the wheel while moving. In fact, you would be amazed how quickly a tractor will flip over on flat land if something attached to your 3pt grabs ahold of the earth. People die when tractors flip, and they flip over when you don't expect them to. If I had a grey market tractor I would sure as hell put a ROPS on it if I was using it for anything that engaged the ground, or if I had a hill, or if I had a ditch, and even if I had a flat piece of land. As for ROPS on antiques, if I used it as a working tractor I'd put one on that too. My antique is used for parades on main street during holidays and pulling kids on hayrides. But if it "worked" it would have a ROPS.