Yes, you have to have the base game in order to play the expansion. As mentioned, you'll need to complete the storyline from 2.55 in order to access the new regions and jobs in the expansion. If you want to be able to take advantage of the new areas and jobs in the expansion I'd recommend getting the full version of the base game now so you can have the story completed or close to complete by the expasions launch.

As for servers, not sure which to recommend but I'd suggest looking at the world forums to see which one gives you a good vibe for what you're looking for.