Well, if you are just starting out, then one stone is fine - anything is better than nothing, which is what many people seem to use!
Without knowing more detail about the stone you have, I'm not sure what I can answer. If I were only permitted to use one stone, I would choose a medium grit. 800 ... 1200 ... I could get the job done. Even without a nagura to make mud, it will still work.
Then I would add a finer stone (nagura is essential with this), and later, a good rough one.
(Also, although I didn't talk about it in the book at all, a selection of different shapes is of course very useful, for sharpening u-gouges, etc.)