Some things I discovered:
Detail gets obscured when you make the gauge too dense.
It’s difficult to use an embroidery hoop once parts of the design are done. (I guess that’s why a frame is used.)
Just like in fair isle, yarns that are different colors don’t necessarily have enough contrast to show up well in the design. On the other hand, colors that are the same value but different colors can be used together for nice shading/depth.
Next time I’ll leave more empty fabric around my design and maybe try my quilting hoop.