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The hands do slightly odd things if "UpDown" is applied on thumb1.  But WW doesn't process hand parts, so that probably needn't be a concern now, if at all.  (Does thumb1 UpDown fit into the class of "unrealistic bending", along with forearm & shin swing?)

I'd say so. In phantom3D's original rigging for the thumb, only two bend axes, grasp and spread, were enabled. When I changed the axis order and redid the rigging, I decided a third axis could be useful for making small corrections to a pose. So basically the idea is that you'd use grasp and spread to get as close to what you want as possible, and then add a little up-down for the rest.

Maybe I should start collecting a set of 'rules' on how to pose Antonia and try to express those as joint limits. Some are simple, such as 'use at most this much forearm swing', but others are more complicated. One rule, for example, might be 'never let the sum of the shoulder bend and swing be larger than 90 degrees'.

But I think testing the rig can proceed without those rules. It's probably better to see what the rig can and can't do and react to that, than to impose limits up front.

-- I'm not mad at you, just Westphalian.