If the OP ever drops in; there are a couple things;
1) Slow, affordable approach: manage expectations; remove the 4-8" stuff by whatever method you have (25-40hp tractor with a loader will work); clear limbs on larger trees up as high as you can get with loader or pole saw to allow sunlight to ground to allow grass to grow; bush hog everything 3" and below; learn to live with anything say 24" and larger; ring out or chainsaw down the 9"-24" stuff; let nature take out the stumps (might need to spray/torch/drill stumps to speed decay/prevent regrowth). Burn everything you can; or dump in low areas, and let it decay. You Might get a few acres per Week (if it's as thick as I picture)
2) Medium speed/medium expense; rent a mid sized hoe (15+ tons) and get to work; once again, leave stuff over 24"; pull/shake/burn all of it you can; but except some piles and just let nature break them down over the years; keep area bushhogged to prevent regrowth.
3) Fastest (still multiple months)/most expensive: hire professionals. It's going to be expensive, and in reality, you're probably going to be discing and raking for months if you want a "clean" field. If you have the equipment, you can do the "finishing" cheaper than them. You're going to need ground men/root pickers;
If there is anything of marketable value; have the loggers take it; but you will have nearly as much clean up as the effort saved; But you might have a few $1k to help moving forwards. You will still have a a lot of raking; rutting; big piles all over that will need burnt/buried/pushed to low areas to rot.
Nothing I mentioned deals with rocks, if that's an issue in your area.