The section of the Great Wall that I visit had some VERY steep steps -- some were as much as about a foot or so high! (See the pic below)
It was sort of like climbing bleachers two at a time in some places.
So, just be forewarned that it will be a very challenging work-out!
Also, from what I remember, you won't have to worry about crumbly stairs or sheer drops off cliffs: dangerous portions of the wall are off-limits. They also have railings and low walls to prevent anyone from falling off and down a mountain.
Really, one of the hardest parts, aside from going up the steep climbs, is coming down them!
Good luck on your adventure!