First 3D Likeness Portrait - Seeking C&C

Strata

This is my first realism/likeness portrait in Zbrush. I'll let you guess who the reference was. This took about a day and a half to get to this point. The hair and poly paint were done relatively quickly just to make it look some what finished. 

I was looking for some guidance and criticism on the piece itself and a few topics if any of you would be so kind.

Workflow
I did the initial sculpt with Dynamesh, then Zremeshed and subdivided up to 15 million points, then put pore detail on. 

Using Reference
I used a lot of reference in Spotlight, though it felt kind of clunky to use. Any tips on how to get the most out of reference in Zbrush would be helpful.

Placing Eyes
I'm struggling to get the eyes to sit naturally in the eye sockets too. It always seems like they're too big or too small and the irises are in the wrong spot. I feel like I'm just fumbling around with them all the time, so any tips on putting eyes in would also be greatly appreciated.

Skin MatCaps
I just used SketchShaded 4 and PolyPaint for these renders. What would you recommend using to improve the quality of the render?

Thanks for looking and fire away!