I like where you are going with this, but I think that the torso is a bit bulky for Dark Eldar. He doesn't look lithe enough for the race. Everyone is using the Dark Elf Corsairs, but if you look at the
Cold One Knights you get a chest piece similar to the one you are using, but a bit more streamlined and the arms from the kit will go with the torso with only hand swaps needed for weapons.
It looks like a great start, though. (Dang, the more I look at that kit, I want to get one.)