Looks good to me -- couple of notes:
If you have an attachment on all the vertices of a muscle it means it may struggle to bulge and produce nice shapes. I'd recommend being conservative with attachments as a general rule to avoid over constraining.
I see all your ribs are combined into one object. If they ever self-intersect it will cause issues with collisions.
You could probably get away with a lower tet resolution on this guy
I see on a few of your materials you have volume conservation on, and also poisson's ratio on. I'd recommend choosing one or the other. Both of the approaches refer to volume conservation and can tend to fight each other if they're both on. Volume Conservation (the attribute) is a bit slower but IMO produces nicer results. If you're using it, you might want to turn Poisson's ratio to 0.
Overall I think you've made really good choices, nice! Be cool to see how it performs on more dynamic animation