Duplification preview with mirror modifier and subdivision surfaces I'm trying to make an object where sides of it interact, when the subdivision surfaces modifier is added. I need all 6 sides of a cube to be edited from a single plane being edited. I want to be able to apply the mirror modifier to the plane to make it symmetrical and the result be duplicated across the sides of the cube. I tried duplication faces, but when I applied the modifier, the cube stopped updating in edit mode and only updated when I entered object mode and when it did update, the mirror modifier wasn't working on the duplicate planes. I also need it to merge close edges and to put the subdivision surfaces modifier on the resulting cube. I basically need a real time preview of what editing the plane, applying the mirror modifier to it, duplicating it to make the faces of a cube, removing doubles and applying a subsurface modifier to it would look like. This is so that I can see how the edges of the cube and the subdivision surfaces modifier interact. Thank you for any help :)
To avoid having a duplicate, you have to delete the side in which will be mirrored before using the mirror modifier. For example, if you want to have a mirrored cube, cut the cube into half first, delete one side of vertices before adding the mirror. That is one way you can avoid duplicates.

After you've got that settled, then add in the subdivision surface modifier as you wish.