Oho, a "Valkyrie", da?
I found this page
that will hopefully help with how a wing should behave, based on the bone structure.
Alsothis site, though in principle slightly squeamish
has detailed photos of bird wings of many types, which should help with appearance of feathers. Personally whenever I drew "Valkyries" I based the wings on Hawks, since it fitted with the story, though you may want to go for Eagles for better symbology, though their feathers are more stark - ergo more difficult to draw - than Hawk's with which you can cheat slightly since they blend together quite well so you don't have to add much outlines.
In general, I always used to draw every single feather then shade them individually. Recently I've changed that to basically drawing lines, then Smudging them + Touching them till they looked like feathers. With Smudging them, there should be no need for black outlines, which should go very well with your style, though I would absolutely insist that regardless of background, both wings should be done in seperate layers. Also, always have in mind where the wing struts out of the back of the character. Personally, though my knowledge on the matter is quite limited, I would place the wings coming out of somewhere near the shoulder blades. There are probably quite a few here that could prove me an idiot though.
Last thing, Loki said to me while I was writing my story that any "Valkyrie" would feasibly have to generate tremendous muscle power to keep him or her in flight, if it were to keep any where near a true-to-real physics theme. My approach as you know was to give them extra muscles in their backs.
Right, that out of the way (
), the sketch looks absolutely fantastic!