I have created a simple 3d engine for my purposes that support texture , vbo ecc....
Now I would create an opengl project that displays scanned a4 documents .
I think to use two triangles that form a rectangle , a plane, then set the scanned image as texture of the plane and send U and S coordinates in a VBO object with only vec3 position and a vec2 UV coordinates.

What are the coordinates that i should use for the plane? pixel? and what is the width and the height?
is sufficent set the width and the height of the plane as a4 for visualize an a4 at video?
and whats are the dpi ? i must take them in consideration? or are only for print?