Not very accurate. The movie exaggerated some parts. For example, the samurai's unwavering loyalty as shown was a bit overdone. In real life, there were internal conflicts among samurai too.
We can recommend a few swordsman and samurai novels.
As for swordsmanship novels, we can recommend Mr. Jin Yong's works, such as The Return of the Condor Heroes, The Eight Dragons, and The Smiling Proud Jianghu. These novels used Wuxia as the theme, telling the heroic stories of the heroes and the grudges of the Jianghu.
For Japanese samurai novels, there was a recommended work called " The Guards at Dusk." The theme of the novel was the Bushido spirit, which described the Japanese's forbearance, reticence, competitiveness, and sense of mission. The other recommended book was " I Was a Sword Hero in Ancient Japan." It told the story of a protagonist who traveled to ancient Japan. He became a sword hero in this era and fought against all kinds of powerful people and dignitaries.
In general, swordsman novels and samurai novels had their own characteristics and charms. The readers could choose the works that suited them according to their interests.
Well, in terms of weaponry, in the movie some weapons were shown in a more glorified way. Fact is, samurai weapons were highly practical but not as flashy as in the fiction part of the movie. For example, the katana was a tool for battle, not just a shiny object for show. And the samurai's code of honor, Bushido, was real but the movie might have over - emphasized some aspects for the sake of drama.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.