You might want to consider an alternate approach. Reading between the lines of your post (and I'll admit I may be way off here), it doesn't sound as though you are primarily concerned with earning income from the acres you would be mowing (such as haying it, or renting it out to someone who would hay it). You mentioned hunting. You'll attract a greater variety of wildlife by not keeping the entire 60-80 acres mowed down to grass the whole time. I have a small section of my land that was once pasture. I mowed it a couple of time per year for the first few years, wanting to keep it open. However, for the past 15+ years I've switched to a rotational mowing scheme: I mow 1/3 of the field once each year, then the next year I switch to another 1/3, and the final 1/3 the following year. Then I start over. I don't always break down the thirds exactly the same way. (Some times I do, some times I don't.) I do keep a few trails through the area mowed regularly. Occasionally, depending on how things are growing, I might skip a year entirely. Any mowing I do in this area is usually in the fall (other than trail mowing) - outside of the nesting season for ground-nesting birds
The goal is to keep the area in a variety of grassland/shrubland/sapling states, providing a much richer variety of habitat for wildlife. I have about 130 acres of mature woods adjacent to these rotationally mowed areas which provides different habitat. Neighboring farms have the pure grassland habitat well covered with their hay fields, so I don.t see the need to reproduce that in any large quantity on my own land. This rotationally mowed area still feels very open, and even something that has not been mowed in 3 years is still well within the capabilities of my 33 HP tractor and 5' medium duty brush mower. (In fact, as long as I haven;t let them get too big, I find mowing a field of fairly dense 3/4" diameter saplings takes significantly less horsepower than mowing a lush field of tall grasses.)
In your situation, you may want to mow the whole thing initially, especially if it's been a while. Though even then I'd urge holding off one one chunk of it for at least a year so as not to completely wipe out that habitat all at once. Let some of your first year mowing grow up for a year or so before going back and cutting the part you skipped the first time around.
If mowing for wildlife is something that interests you, it also may change your approach to equipment: Mowing 20 or 25 acres once (or maybe twice) a year is a whole different world than mowing 60-80 acres two or three times a year. You may want to hire someone to do that initial mowing for the first year or two, but after that, you can easily keep up with things with much smaller, less expensive equipment. I can mow a couple of acres an hour with my set up - maybe down to 1.5 acres/hour if things are really dense. I actually enjoy the time I spend on the tractor mowing. However, I'll admit it helps that I'm not doing anything near 60 acres.
Regardless of what strategy you choose, the size equipment you end up with will depend on your own personal preference for trade off between spending more time or spending more money. 20 acres with my compact tractor would be 10 hours of mowing in my conditions. If there were a lot of obstacles (rocks, trees, etc.), it would take me a bit more. a 40 HP tractor with a 7' brush hog would speed things up a bit: probably around 3 acres per hour.
For me, the added benefit of rotational mowing is that it frees up a lot of time for me to work in the woods, which is really where I like spending my time: harvesting firewood or saw logs for a project (usually bartered with a neighbor), improving wildlife habitat and timber growth, and maintaining our trail system