Hi David Anderson, thanks for the great idea on how to attach my SL file - I have gone ahead and done that.
With the layers, the issue I had is they were not maintaining the intended depth order. I sought to have the human systems go Skeletal, Nervous, Respiratory, Circulatory, Digestive and then Muscular on top. This works with using states - the systems are always in the correct order so if you select them all Muscular is on top. However, when I used layers, the system that was on top was always the last one selected.
I attached my SL file to the Resources tab to download and look. You can also find my attempt using Layers instead of States by clicking Next and viewing it on the 2nd slide in my Review 360 link.
Thanks for any help!
Edit: My colleague just sent this old community thread to me and it sounds like a solution is listed within it for how layers stack.
https://community.articulate.com/discussions/articulate-storyline/slide-layers-and-stacking-order