A land plane, grading scraper or land leveler (different names for the same thing) is a way better tool for gravel driveways regardless of skill. There's quite a significant weight difference between the GS0560 and GS1560 models i.e. 350lb vs. 525lb. The GS0560 should be a good choice for your needs but that's not to say that you could have a good experience with the heavier model. I would suggest 5ft over 4ft though. What is the dealer saying? Look at Land Pride's website and check out the "Kubota Matched" option.
www.landpride.com
For the record, I have and use a 7ft box blade and 7ft land leveler, both from Everything Attachments, and the land leveler is way better on the gravel driveway.