It starts at a specific point in the manga, but I can't recall exactly without looking it up. You might want to check some manga forums or dedicated fan sites for the precise chapter.
Gomi Gojo's Territory Opening Gesture was an important element in the " Return of Curse ". Gotto Gojo's domain was displayed as 'Boundless Empty'. This gesture was to pull the enemy into the infinite inner side, forcing the enemy's brain to produce a large amount of information, causing the brain to lose its function and could only stand and wait for death. Although there was no specific description of the hand gesture, it could be speculated that the hand gesture was to expand the domain through a specific posture of the hands.
Sukuna does die in the manga. The way it happens is quite dramatic and ties in with many other elements of the story, adding depth and tension to the overall narrative.
No. Ryomen Sukuna is a fictional character from Japanese mythology and modern manga/anime. He doesn't have a basis in a true historical event or person.
Nope. Ryomen Sukuna has no basis in reality. It's a product of the creative minds of the writers and illustrators who designed a captivating fictional character for the enjoyment of the audience.
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.