Dear ExMachina, I really appreciate your work, I think it's awesome. Really, really nice.
So I'll leave a comment but please take it maybe as a suggestion (or maybe not, it's your imagination which guides the pen):
When I think of Wit (not Hoid) I imagine a tall, slender guy with a wiry facial expression without being too muscular. I would think him to be more of a scholar-like stature in a uniform (thinking of various scenes where he is described and it made me think "why is he wearing that sword?" - for me, it just didn't really fit to Wit, maybe because he's so much "over" the normal/physical actions in TWoK). I know that his age is difficult to tell, but his knowledge makes me want some tiny wrinkles in his face, not at all to make him look old, but for some life experience.
For the uniform: I did actually imagine the inner collar exactly as you did it, but I find the outer collar too big and protruding. Maybe a straight-cut, tight, not-so-voguish uniform. Plus maybe I would even give Wits uniform a little worn look, still being pitch-black. (I hope there's no discrepancy here.)
Probably it's most difficult to get a right shot of those characters that are not described so often. The vision might be so different for various readers. So what you do is great work!
One last thing - if you ever happen to look for new to toics: I'm a Zahel fan. Would be so awesome to have a good drawing of him!