As a WoW player I've learned the impact your choice of server can have on your experience.

To what extent are the worlds separated from each other in FFXIV? For example in WoW you can have characters from different realms play together for some types of content but no cross-realm guilds or high-end raids. The XP bonus for starting on a new world is tempting and transfers don't seem to be nearly as expensive in FFXIV, but do you actually encounter players/communities from other worlds?

Also, is there are any particular world (or data center) with a concentration of Finnish players?