Making an Assassin costume is definitely in my top 10 things I want to create, so I'm somewhat in the same boat as you (minus the deadline and such). For starts, here's a site that has good basic references for the general costume. It also has a lot of other series artwork that's amazing for references, most of them with good resolution so you can pick out details better, but here's this for starts:
Another good way to pick at the costume is if you can get ahold of the figurine so you can get a 3D up close examination of it!
I'm still hunting for the layer-by-layer references myself. ^^; But if I find other ones, I'll toss what I do find up here!