You could code this all yourself with some clever scaling, or
the MagicCam plug in will handle all the zooming you want to do. http://bit.ly/1agM2QH
For the black background/ crosshairs. You will want a layer with all your assets that is Invisible by default.
So, the basic flow will be:
When Space is pressed > Show Layer > Activate Cam
Press button > Zoom in
Press button > Zoom out
When space is pressed > Hide Layer > Deactivate Cam