Welcome back, Graz. I think your listed out plan is pretty solid. The choice of what single implement to purchase is not an easy one. Personally I find a rear scraper blade and box blade to both be essential tools with different functions. The land plane is really only for gravel driveway maintenance or other loose-material smoothing; a one-trick pony, if you will. Some people like a landscape rake for driveway work, and I don't doubt that they can pull gravel around, but I could see one struggling to be effective with the large stones you have. They just aren't very heavy or strong tools.
Your location of SE presumably means south east, where you don't have snow to deal with in the winter.
For me: the
box blade is on almost all summer long. I do my landscaping stuff in the summer, and otherwise it makes for quite compact and heavy rear
ballast, keeping the tractor maneuverable and the loader work safe.
The
rear scraper blade is on all winter long, for any snow plowing duties, and in the late fall and early spring is when I find I need it to dress my driveway and re-shape the crown. A box blade can only pull forwards - the lack of side-to-side angling makes it less productive for some driveway work, like fried1765 likes to so often point out.
I would try to get both implements. Kind of surprised you don't have either already, with the type of work you need to do. If you search your local craigslist and facebook marketplace, you can probably get a solid rear blade for a few hundred bucks, and a nice box blade for several hundred or so.
