What regular maintenance is best for a Japanese knife?
As I am sure you can tell by looking at it, your Japanese knife is primarily sharpened only on one side.  As a result, the cutting edge is angled more steeply.  Japaneseknives on Wordpress has some simple pictures illustrating this.  This asymmetry is why you can't reliably use a honing rod on it, which relies on swipes to both sides of the edge to keep the blade smooth and free of burs.

The steeper angle makes the blade sharper, but you could say it is a double edged sword that can also make it prone to wearing more rapidly, depending upon how it is treated.  As a result, sharpening only once a year may not cut it.  There is another page on Korin's website that might be more helpful to you, including an informative video.  L'Ohira's Knife Care &amp; Sharpening page has some good tips on the type of kit you might want to use, including 3 grades of water stones, though you may or may not need the course all that much:


Arato: A coarse grit stone used mainly for damaged edges and for creating new sharp edges.
Nakato:  A medium grit stone used for minor repairs and creating  sharp edges.
Shiage:  A fine grit finishing stone.


Much of that information is also covered in the Korin sharpening video.
Also, since the knife is carbon steel, it can rust.  Based on your question, it sounds like you probably take good care of your knives anyway, but you should especially make sure you clean this one promptly when dealing with acids.