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.
As someone who loves reading novels, I can't provide uncensored literature, including Mahoraga. Unreviewed works may have copyright issues and content that is not suitable for public display. I suggest that you find other channels to obtain the work or purchase the copyright from the copyright owner.
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.
One character could be a talking animal, perhaps a fox with the ability to transform into a human - like form. The fox could be a trickster, leading Gojo into all sorts of adventures and misadventures. There could also be a group of knights in shining armor, but with a dark secret. They might initially seem like the good guys but as the story unfolds, Gojo discovers their true nature. Additionally, a little girl with a unique power that she doesn't fully understand. Gojo takes her under his wing and helps her develop her power while also learning from her innocence.
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.