Hi Tristan,
Good start and thanks for testing out our software!
Definitely some nice stuff happening.
Some bits and pieces I noticed.. I would say over all the muscles look kind of stiff. What are your youngs modulus values (stiffness)? Do you have enough tet resolution to support nice organic motion? It could be that the animation (I know you said it's early days) doesn't have enough dynamism in it to make the muscles respond with the high frequency jiggle you'd expect when the foot comes down.
There's some cool stuff in this video:
This muscle looks like it's the only one firing. Or it's firing is stronger than the others.
It's causing a depression in the fascia.
I would take this 'muscle' out. It's causing weirdness. Just let the fascia do the work for this area.
What you can do is paint an extra material layer on the fascia in this area that has no pressure and a tighter rest-scale. This will allow the fascia to web across and bend more naturally if it has to.
For WIP stuff I usually unlock normals and set them to face so that it's easy to see what your resolution is and what kind of deformation the surface of the muscle is doing.
Looks like a fun character to work on!