Crisis on Infinite Earths in the comics concludes with a battle of epic proportions. Heroes unite from different realities and, in the end, the fabric of the multiverse is altered in ways that have long-lasting effects on DC Comics.
The main way it ruined DC Comics was that it threw the established order into chaos. It made it hard for new readers to jump in and for long-time fans to keep up. Plus, it seemed to sacrifice character development for the sake of a big event.
In Crisis on Infinite Earths comics, not many Supermen die. Usually, it's a limited number, and the focus is more on the overall story and multiverse chaos.
One idea could be exploring the backstories of minor characters during the Crisis. For example, how the normal people on different Earths are coping with the chaos.
In general, the Crisis of Infinite Earths didn't incorporate characters from other comic companies. It stuck to its own established characters and storylines.
It's hard to give an exact number. There were quite a few comics involved in this storyline, but it varies depending on how you count related tie-ins and spin-offs.