Kahhori isn't in Marvel Comics. Marvel has many well-known and established characters, but this name doesn't ring a bell among them. It could potentially be a new or lesser-known creation outside of the Marvel realm.
They contribute in several ways. Firstly, they keep the fans engaged between movie releases. They also introduce new concepts and ideas that might later be incorporated into the movies. For instance, some new villains or plot twists can first be tested in the graphic novels. Also, they can provide different interpretations of the characters, adding more dimensions to the overall MCU franchise. Moreover, they can attract new fans who are more into reading graphic novels rather than just watching movies.
Not always. While the MCU draws inspiration from the comics, there are often changes and adaptations made to fit the cinematic universe and modern audiences.
The origin stories give depth to the characters. Captain America's origin, with his roots in World War II, adds a historical and moral weight to the MCU. His values shape his actions and influence other characters. Also, his origin story allows for interesting time - travel and alternate - reality plotlines later in the MCU.