I think the composition of the model looks a bit top heavy when she is wearing her helmet. Adding some additional - swappable shoulder pads and maybe a couple elements on the hips, side of thighs that match the sci-fi look of the helmet would balance the model a little bit more.
I also noticed you mentioned breast bones, however if using the standard animations or mocap as you have suggested - those bones will not be animated. How can these bones be animated - without the base (standard/mocap) animations including breast motions?
Perhaps setting the bones to be controlled by physics?
Overall the model looks very nice. I especially like the look of the helmet.