No doubt you've had enough of the notifications by now but hope the following helps with your last question.

Problem with adding a mask direct to Ezskin mat is the complexity of the node set-up so layer is probably a good place to start however it has its own problems. Thought I'd do a quick example of layers with Firefly but didn't seem to work so this is for Superfly.
Create Mask

Apply Ezskin to figure

Add new Layer to skin mat, add new material and apply mask

Render...

This will create a lne where the mat ends with other textures which I think is due to the SSS. Solution appears to be to add the layer to these adjacent textures.

Render again

The layer just replaces the mats below so if you require effects like bump to propagate through its a bit of a problem. I use a much simplier texture set than Ezskin so just copy the bump onto the new layer but for Ezskin that is more complex.

Hope that helps with the ideas