Sadly, I will say I'm not entirely sure of this, but from what I've noticed of tangent maps, they're sort of like a texture (for lack of better comparison) that defines HOW the model reflects things, should it be reflective at all. So if you load up sins, and create a ship you know is pretty reflective, and just look at how those reflections look in the game as you move the camera around the ship, then go and alter the ship's tangent map, when you load it up again, things will look different. It certainly effects shields, since all they have is a tangent map and no textures.
Now, again, I could be wrong about that, or that could just be only part of what they are. But it's just what I've observed with playing with them while making ships myself.
For your number 2, StCobalt's links are pretty useful. I know less so for the second, since I don't use 3ds max, but the channel guide for the different .dds files should help you a lot on that first post.