As always, wise and sage advice from the members on this board. I have no particular opinion on the size of tractor you should purchase, and the only point of reference I can work from is my personal situation.
I mow 5 acres every week, bush-hog 2-3 acres every month, and bush-hog a neighbor's 5 acre field 3-4 times a year. Not quite as much as you need to handle, but a good sized job none the less. I use a Kubota
B7100 HST with a 5' mid-mount mower and a 4' Land Pride bush-hog. The tractor handles the chores just fine. The terrain I bush-hog is a bit hilly and although it takes a bit more time with the 4' cutter, I don't view it as a problem. I usually spread the mowing tasks over a few days every week so I don't have to spend 4-5 hours straight on the tractor, unless I get behind for some reason. I like to play golf, too.
Why a
B7100 you might ask. I grew up on a dairy farm and view a tractor as nothing more than a tool to do particular jobs. When I bought the Kubota a few years ago, I decided how much I wanted to spend, and shopped around until I could fit that tool budget. A bigger more powerful machine would be nice, but I wanted to spend my $$ on other things, too (read that Mustang GT). I really didn't need a bigger tractor. You may decide you do need a larger machine, but, a
B7100 will do what you have to do, and more. Heck, you might even want to put the money you save toward a new Mustang convertible like I did.