Importing external movieclips?

I’m making a game where I have a lot of movie clips that I need to load so I was wondering wheather ActionScript 3.0 allowed us to load external movieclips?

Can we import an external display object (movieclip) into a display object container?

Or do I have to load a .swf which contains the movieclip onto the stage?
What happens if I need to pull in multiple .swf files can the movieclips overlap or will one .swf file block the user from viewing the .swf in a lower depth?
Can I import the movieclip from the external .swf file from its library and add it to the main stage rather then adding the whole .swf to the main stage?

Thanks in advance.