I'm interested.

I don't care either way on a guild-type format, but it takes second priority to a good plot-hook and some interesting villains.
If I were you, I'd look to samurai cinema for inspiration; films like Seven Samurai can be the source of a good adventure for your players. In a lot of cases, however, a guild becomes unnecessary or even burdensome. Adventuring guilds are a staple of D&D and other western stuff, but aren't necessary depending on the plot.

If the game takes place during a war, for example, you don't need a guild, but you'd do a lot better as part of a standing army or even a group of mercenaries.

Another thing you should decide is the era. Even if this is largely a fantasy game, you should take note of the year, because Japan's history has a huge influence on its stories. Sengoku and Bakumatsu are both popular war eras, but have different overtones due to what was happening and even Japan's interactions with the outside world. Edo and Meiji are popular peacetime eras, but also have different flavors. Edo is better for the quintessential wandering samurai, whereas Meiji often deals with the decline of the samurai. Even the first few decades of Edo are different from later years.