Saitama's strength in the manga comes from his intense training and unwavering determination. He pushed himself to the limit every day, which eventually led to his overwhelming power.
It expands the universe by exploring the backstories of the characters more deeply. For example, we might learn more about the childhood of characters like King. It also creates new scenarios for the heroes to face, like battles in different dimensions. This gives more depth to the world of One Punch Man.
The One Punch Man manga has been running for quite a while. As of now, it has multiple volumes and chapters, but the exact length can vary depending on how you measure it.
Well, it's hard to give an exact number. The count keeps going up. You might want to check the official publisher's website or some well-known comic databases for the latest and most accurate count.