As a novice, I can't claim much knowledge about tools, but from what I have read, Japanese tools can be wonderfully made. There are different grades of Japanese tools - some are mass produced, while others may be exquisitely handcrafted, and much in-between. I have been to Japan on extended business trips (several weeks at a time).
From my reading, I learned that it takes matching experience and skill to take advantage of the highest quality handmade Japanese tools. Few people are qualified to take advantage of the highest grades of Japanese hand tools.
I do have a two-sided 1000/6000 grit Japanese water stone that I bought for less than $20 from Amazon. I use it as the final stage after courser grit diamond stones. I knew I was buying a cheap water stone, but I don't know if you can find better quality water stones in Japan, or what "better quality" means in the context of a water stone.
If I were you, I would be looking for chisels, hand planes, saws, and other quality steel tools to bring home. I think that the water stones are more easily obtained at a reasonable price in the US.
If I were you, I would be sure to understand the different types of Japanese tools, how to tell quality from "overpriced", and how much they cost if you were to buy them here, so that you can recognize bargains when you get there. In other words, get some learning first, and have a plan.