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.
Naruto would become more confident. Gojo's power is extremely strong, and having it would make Naruto feel like he could handle almost any situation. He'd also become more strategic as Gojo's power requires a different approach to combat compared to his normal ninja skills.
A possible plot is that with Gojo's power, Naruto is able to see the world in a new way. He can now perceive curses in the ninja world that were previously hidden. This leads to a whole new side - quest where he has to deal with these curses while still maintaining his duties as a ninja. He might also use Gojo's power to teach other ninjas a new way of fighting, changing the ninja combat system.
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.