I think the a frame level is a better way to find your contour. My project was much smaller, but I was able to mark the contour by myself.
Here is an article about the a frame level.
I used construction flags for my markers.
Like these. The feet of my A frame level was about feet wide. I used a flag at each foot, and eyeballed the center of the contour for my flags to be 18 inches apart.
Here is my tiered wattle garden thread. Spoiler, my wattle was mostly structurally sound for only two years. Now at the four year mark, my clay is sill sorta holding shape. The wattle is scattered sticks. But maybe you can use this info and Williams tiers to figure out something that is more permanent than mine.