The metal effect really looks nice, and I'm looking forward to seeing it in game.
By "control surface hinge areas" I meant the line formed where a control surface (aileron, rudder, elevators, etc) attach to the plane. These moving parts would have a bit more separation and so the line where they attach should be slightly darker/deeper looking. Lots of guys add a shadow effect there too.
That little grey triangle is something from the 3D texture itself I think - all you can do is try and cover it up - it might take some trial and error.
Can you post a pic of the original aircraft?