Linking/moving "Pictures", "Movies" and "Music" folders to external drive...

Hello!

I was concerned about not spending too much money when boying my Mid-2011 iMac 21,5" 8GB RAM, 500GB HD, so I went for the smaller harddisk.

Now I regret this, and would like to move all my pictures, videos and music to an external drive, but yet have all files accessible in the folders "Pictures", "Movies" and "Music", as today...

Can I (1) make a permanent link from these folders from the built-in hard disk drive and to corresponding folders on an external drive, and (2), how do I go about doing this?

Otherwise, (3), what would be the implications of cloning the internal 500GB disk, and replacing it with a larger one?

Best Regards...