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.
Occasionally, Hulk can take control of Banner. This often happens during intense emotional or physical stress situations. Different comic arcs handle this differently, but it's a common theme.
In the manga, Sukuna doesn't possess all 20 fingers. There are specific story arcs and events where his finger count changes based on the plot developments.
In the manga, Sukuna does acquire all his fingers over the course of the story. This is a significant plot development that has major implications for the storyline and character dynamics.
It depends on how fast you read. If you're a fast reader and can finish a short story in 30 minutes, and assume an average story length, it might take about 25 hours or so.