That tractor is 28 hp, with 21 hp at the PTO. That grass looks thick and coarse. You have a lot to do.
Since all you want to do is cut the grass, I would not consider, this late in the season for Newfoundland, plowing. Find a bush hog and expect to cut with 3 foot bites. I don't think the tractor can handle any more, even in low range.
Other posts speak to how to set up the bush hog for most efficiency.