Tire choice is always a hot topic for debate. I have the R4's and they have been a good all-around choice for my SCUT, but I do not use it as my primary grass cutter. My tractor is in the woods clearing/maintaining trails and rotary cutting small fields and maintaining a very long gravel driveway primarily, with the occasional soil moving. In my soil, the R4 tires will mar the surface of the soil a bit if the ground is even a little damp. And since there a two subsurface sprins/seeps in the area I mow, that's a problem for me almost year-round.
I'm a big fan of the box blade as an item you can get a lot of bang-for-the-buck, but some people hate box blades. Problem is, its hard to know how you feel about it unless you spend some time with one. For me, it has been great at driveway maintainance and good at moving and breaking soil. It does OK at moving snow (though I like the FEL more for that), and does a great job of breaking up packed sleet/ice from the driveway. A box blade sized for your machine will probably come with 4 adjustable shanks. Remember, you don't have to engage all 4 at the same time. Use only one or two if you initially have trouble breaking soil. We use the box blade to break soil for a garden without a rototiller, and it does a pretty good job. Not as good and pretty as a tilled garden, but the veggies don't seem to mind. And I can tell you from experience, you can only break up roots to a certain size. Your machine is too light to move mountains, even if it has a high power-to-weight ratio. If your shanks engage roots too large, your light tractor will just spin its tires.