Fading out a material according to angle and proximity

I have a quad with a texture on it that I only want to be most opaque when the face of the quad is pointed directly at the camera. As the camera or quad moves so that we're looking at the quad from an angle with one edge closer to the camera than the other, I want the material on the quad to start becoming transparent, until it goes invisible when viewed at a 90 degrees.

Similarly, if the camera comes within a certain distance of the quad, I'd need the quad to fade out as the camera approaches, and become totally transparent by the time the camera clips with it.

Is it better to use a shader or a script attached to the quad to do this?

If I used a shader, would that shader also affect particles as the camera moved around them or approached them?