Rear Finish Mower Bush hog or finish mower

[IslandTractor]

You haven't considered a medium duty flail mower? That would be perfect. Cut is much better than with a bush hog, much tougher than a finish mower and it is safer and easier to store as well. Most people forget about flails as the major US manufacturers build mostly heavy duty models designed for roadside maintenance and those are very expensive. For less than $2000 you can have an excellent Italian flail (Caroni TM1900) delivered to your door by AgriSupply in North Carolina. It will cut just about anything a medium duty bush hog will cut but the cut itself is only a little worse than what you'd get with a finish mower. Way less noise and way way safer than a bush hog too. Only real negative compared to a bush hog is that you actually need to grease the bearings every six hours of mowing (a three minute procedure) and replace the drive belts every few years (a half hour procedure). It is certainly much less maintenance than a finish mower used in the field. There is lots of reading on flails here on TBN: try the "Let's talk about flail mowers" thread. (not sure if that is the actual title but something like that....days of reading on all aspects of flail mowers).

 

[Ford850]

I'd get a bush hog, but make sure you research it to determine the lowest cutting height. Some cut at a minimum of 4-5" which means you have to drag the sides in the dirt to cut and it still won't look like a lawn. Look for one that cuts 2" or less. The real advantage of a bush hog is that if you keep up with the mowing it will give you a cut that is close to a lawn. And if it is wet or your tractor is down for weeks while the 5 acres grow tall again, it's no problem for the bush hog. With a finish mower you will have a mess every time the grass grows too tall between cuttings or when it's wet when you mow. Tall grass and weeds are also rough on the spindles of a finish mower.

 

[beenthere]

You said "pasture overgrown with weeds".
A finish mower will work quite well for that.
I have about that many acres that was pasture overgrown with weeds, and I mowed it initially with my JD 54" mmm and JD 445 lawn tractor, and keep it mowed in nice lawn every couple weeks on average.

I've used the rotary cutter in place of a mower, but wouldn't classify it as much of a hit for lawn look. Finish mower or flail mower would be my suggestion (rent a rotary for any initial brush cutting).
You've a lot of good suggestions, and I'm thinking you could make any of them work for you. But in the long run, I suspect you will end up with a finish mower.