Touch up stone

Would the Zulu Grey make a good touch up stone?

I have some Barber's Hones but have never used them. My sense is that the technique required on them is not so simple as it seems, while a Naniwa SS 12K, for example, requires little more than keeping the blade flat and doing just a few passes. Starting with the Naniwa makes sense because it will eventually take its place among the 1K, 4K, and 8K as a complete honing system.

I would suggest a Naniwa 12k. Simpler to use for a beginner and more likely to give you consistent results. Once you acquire your set of hones you'll want the 12k anyway as your finishing hone.

I'll agree on the Naniwa 12k or any such "normal" stone.
If you get a barbers hone or something exotic it's harder for people to help you since nobody knows how you hone behaves.