I would certainly include a story that showcases a Japanese craftsman. Those are always my favorite. I would probably choose Kite Story.

I would probably include a story with Gen because their banter is at the heart of the series. Perhaps their first meeting in Bounty Hunter.

And I would want an issue featuring a formal duel of some kind. I would probably choose The Way of the Samurai. Or perhaps The Duel.

And for a simple touching (if sad) story to include, I like The Music of Heaven.

I'm inclined to disrecommend Chanyou for such a thing. I think it's perhaps the best Usagi story, but not what I would use for an appetite-whetter. In part because it's the pay-off to years of stories between Usagi and Tomoe. I imagine such an edition would want to stand as much alone as possible, and spoil as little as possible. But also I really think it is the best of the series, and that's not where you want a reader to begin. It's what you want them to build to.

For the same save-the-best-for-later philosophy, if I were to include the first part of an arc as a cliffhanger, I would likely look to Dragon Bellow Conspiracy before Grasscutter. The opening chapter is much more cliffhangery anyway. The first two chapters of Grasscutter convey fairly complete mythological tales and anyway don't even feature Usagi!