1) the higher the grit the finer the edge. The 4/8 is more versatile but the 12k leaves a finer edge. The 12k will do more than most think with a little effort.

2) All of the above. You can go from stone to crox to bare strop, stone to bare strop or crox to bare strop depending on what the blade needs. If I was only choosing 1 option it would be the stone as it is easier and quicker and capable of more. A hundred laps on linen and leather tend to take any harshness out of a stone edge if you find it.

You can also keep the stone for only when the crox seems to be loosing effectiveness and use the crox as your basic touch up method. A good crox stick/paste/ powder buy will last you a lifetime and can be used on many readily available substrates.