
I think stage 2 is bigger than stage 1 and possibly has multiple starting and ending points, or maybe there are multiple stage 2's with the same difficulty. I also think there is something like this because not every team will clear a stage in the same amount of time. It will especially become troublesome when the difficulty rises and clearing stage 2 in exactly the same time as the people in stage 1 clear the stage and progress to stage 2 will become impossible because another team is still occupying the stage. So I think stage 1 is the only stage that only has 1 group at a time.

No, remember the chapter they said the stages were created over an original map? That ruin was part of the original world that who ever is the master of the stages laid their map down that is able to be reset after each clear. I'm sure we'll learn more information about the original world as things go on.
Apparently while the mc was like progressing throughout the story, he stayed within stage one, and you know how like the stage was reset multiple times and new participants arrived like many times while he was still within stage one? Are the friends from the beginning STILL in stage two? Idk how stage two works..