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.
It could be other elements from Japanese folklore. There are many supernatural beings and concepts in Japanese mythology that might have influenced his creation.
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.
Sure. Fanfiction is all about creativity and exploring different ideas. Izuku creating quirks can be a really interesting concept. It could be related to his own growth and development, or perhaps it could be a way to help others. For example, he might create quirks to give to those who were born without any, which would be a very heroic and selfless act. It also adds a new layer to his character, showing his intelligence and innovation in a different light.