On the grindings, we use it in our equipment staging area, really depends on the grinder, some of it is like raw material, others have huge 3" to 6" chunks. If it is finer material it packs really well, cows hooves may tear it up. I put 3/4 rock around the water tank, by the end of winter it is dirt, but they don't sink in it any more it is solid.
If you put down 4-6" of grindings packed it down then 4 inches of granite or base it should make make for a solid foundation that you can still drag, plus crown it so the water runs away from the pen and it should help.