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.
Well, they might be really shocked at the power levels of Goku and Broly. RWBY characters are used to their own kind of battles, and seeing the insane energy blasts and transformations in the Goku vs Broly fanfic could leave them in awe. They might start thinking about how they could incorporate some of those powerful moves into their own fighting styles.
Some of the RWBY villains might be intrigued by the strategic elements in Red vs Blue fanfiction. In RWBY, they are used to battles with semblances and dust, but in Red vs Blue, the battles rely more on regular weapons and teamwork in a different way. They could analyze these new strategies and perhaps even consider applying some concepts to their own plans in RWBY, if possible.
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.