To adjust the backdrop size, use:
Oddly, only one Render Layer node gets "Mist" added to it when you enabled Mist in the Passes panel. If that Render Layer node happens to be inside a Frame node, duplicate it, and remove the duplicate Render Layer node from the Frame.
Like "unparenting" two objects, press Alt+P
Your object isn't aligned with the Cartesian coordinates. You'd like to view it in Edit Mode straight-on, without changing the objects orientation. Press-and-hod the Shift key while pressing the normal viewing keys. For example pressing Shift+Numpad1 will align the view to the object Y-Axis (front-to-back).
See "It is hard to see the "how to" in the context you describe, but here is an approach for rigging the eyes." for better answer.
When Animating the Eye with the “Track To” Constraint, the location of the mesh changes. How do I fix this?
Swtiching Workspace panels (e.g. Default, Shading, Compositing, Layout) use CTRL+PgUp and CTRL+PgDn