If you are wanting to simply crop the sides put everything in a movieclip and enable the "Use runtime bitmap caching" checkbox (visible on the bottom right when you have a movieclip selected).
Sadly I don't believe there is any way to get things to go with a position from the middle by default. It always starts at the top left begin (0, 0). One thing you could do is try adding some code (something like that posted below) and see if you can get ti to tie into all the movieclips and other content automatically without you having to work at it.
CODE
var s_height = Stage.height;
var s_width = Stage.width;
//tie in positioning to something like so:
n_x = s_height-(s_width/2);
n_y = s_width-(s_width/2);
The above code basically sets it sow that n_x and n_y are 0 in the middle of the stage. Then you just have to place all other items relevent to n_x and n_y to have a standard graph layout.
If that is more than you want to do with code you could always just create a blank movieclip that you place in the center of your stage, that way (0, 0) is in the center of the stage (relevent to the movieclip) and you can place everything else inside the movieclip to make it easy to use adn have the standard graph layout again.
Hope that helps.