Do not buy a dozer to clear land. It's probably the very worse machine for clearing land ever used. Years ago, they where popular, but labor and fuel was cheap, and everyone had a big dozer sitting around to use.
The only thing that is effective at clearing land is an excavator. The bigger the better. Do not even try to clear that much land with anything under 20 tones. That would be the starting point. It's big and powerful enough to take out any trees, and fast enough to make it worth your time. If you can find a 30 ton machine, that would be even better.
What everyone seems to be missing is what do you do when the trees are out of the ground. It's easy taking them out, it's very hard getting them to the burn pile. A dozer with a root rake takes forever to take out a tree, but when the tree is on the ground, it's even worse at piling them up to burn. Even with a rake, you will get massive amounts of soil in your burn pile. The dirt slows down the burn, and it builds up so quickly that you will be left with mountains of it at every burn pile to deal with. The excavator can pick up the entire tree, root and all, and put it on top of the burn pile. This way it burns cleanly and quickly.
That would be step one.
Depending on your soil, what you want to grow, and how much time you have, you can sell the excavator and buy a dozer to clean up the land after it's cleared. A dozer is good at this. The bigger the dozer, the faster you will get it done. Mine is 170 hp, and it's pure torture after a few hours, but it does move a lot of dirt fairly quickly.
Once you have the land graded, then you can sell the dozer and look into buying a tractor to farm the land. Not knowing your crop, or how much time you will have to till, plant and harvest your crops, I would suggest starting out with something over 100 HP with 4 wheel drive. It doesn't really what brand you get, at that size, they are all pretty much the same. Just buy something that you can get parts for when it breaks down. The more HP you have, the bigger the implement you can use, and the more you can get done in a day.
Avoid shortcuts, and especially anything that looks like a neat or clever idea. Stick with what's been proven to work, and what is used on big commercial operations.