Two wheel drive will do a lot of work when equiped with loaded R1 tires, 4 wheel drive units usually have R4tires but will still go more places in 4wd than a 2wd unit. 4wd is great for loader work but a 2wd unit does just fine.
The difference between which one to buy is a gut call, when and how you want to use tractor. As far as the disc vrs a tiller, i spent most of my life plowing and disking and now I use a tiller. Plowing and disking is fine but I enjoy the tiller way more. I don't do as large of an area now but the tiller is 5' wide I really would like to get a 6' one but what I have works fine, and at 5 foot at a time you can get a lot done quickly and way faster than plowing and disking with one piece of equipment, although every so often plowing should be done to really turn over the soil.