If you're sure you want to use bench stones as opposed to some sort of tool... You'll want at least three:
- Coarse for profile and/or repair;
- Medium-coarse for sharpening. I.e., drawing the first burr, chasing it, and possibly deburring; and
- Medium-fine for either drawing a refined burr, chasing it, and deburring.
You won't use the coarse stone very often, and considering that nearly all MACs come with a very good factory edge, you probably don't need one now. In fact, unless and until you've become pretty darn good with the two finer stones, I suggest not using the coarse stone at all. Mistakes made with coarse stones can take a lot of work to fix (or a lot of time to wear out), and it's a good idea to wait until you can hold a nice, steady angle before trying them on your good knives.
As a generic, I like the Bester 1200, and either the Suehiro Rika or the Arashiyama (aka Takenoko) as the two (high quality and not inexpensive) medium stones, with the idea of adding a Beston 500 later; and also recommend an Idahone 12" fine (aka 1200) ceramic "steel."
By way of comparison my water stone bench kit is (or was) relatively "cost no object," and Beston 500, Bester 1200, Chosera 3000 and Gesshin 8000. If I ever wear down the first three, I'll probably replace them with a Gesshin 400 and Gesshin 2000 if the state of the art doesn't change very much. But I consider the Gesshins to be too expensive to be a good practical choice for someone who isn't deeply committed to the best possible edge. Besides 8K is overkill for a MAC, anyway.
A Rika or Arashiyama is a more practical finish. Because the Arashiyama is at the limits of a MAC Pro's ability to hold a polish, it might be the better choice -- but the Rika is plenty fine if you stay with it until the "mud" breaks down. I'm partial to the Arashiyama, but you can get a Beston, Bester, Rika three-stone combo from CKtG at a very favorable price. (Please note, I do some paid writing for CKtG
King stones are a deal less expensive and pretty good -- but not nearly as fast or consistent as the stones already mentioned. Norton water stones are also very good, but they're not as good as the already mentioned stones either, and as -- if not more -- expensive.
Hope this helps,