I played Guild Wars a year ago and now I want to start again

I began playing GW on the Nightfall campaign and recently I bought the Complete Edition box with all stand-alone and Eye of the North.
I'm more the PvE player and I have a question about it.
I'm wondering since a long time, can your characters travel between the different campaigns?
To specify, I'll give an example:
My first character (a lv 20 Warrior) was created in Nightfall. I'm certainly not done with this campaign, but is it possible that I can do the Prophecies or Factions campaign with him? Or do I have to create a new character for those campaigns?
What I mean is; are characters bound to a specific continent?
Then the second part of my question: IF we are able to do all campaigns with one character, is it possible to go with a Dervish or Paragon to Cantha, or with an Assassin or Ritualist to Tyra?
Thanks in advance
