Nice work, glad your interested in Ziva
I'm sure since you will start making iterations on your simulation, you start to adjust your model
Here some suggestions that can help you before you start
Separate calf muscle to 3 shapes: tendon, medial head and lateral head
Make muscle shapes more smooth by removing boxy shapes ( this will affect how good your musles will look when flexed )
Make rectus femoris more streight and separate it in two muscles: vastus intermedius and rectus femoris
If you are aiming for the knee shape I would suggest making meshes around it to represent tendons and ligaments but do not make them too thin
Hope this helps ! Looking forward to see your results !