Sorry, but if growing succulents, we don't want any wetting agent in our mix, just the opposite. I'd ditch the worm castings as well, too rich for C&S. Let folks fertilize as needed in THEIR control.

I agree with Karen's post. Have you considered having bulk bins of components available at the garden center rather than selling your own pre-bagged mix? You could post graphics by the bins showing pictures of and explaining recommended mixes and why they work while still allowing people to customize for their specific conditions. Also, train the employees so they have at least a basic understanding of the components you're selling.