I heard a reviewer saying with some certainty that you would be able to use an existing level 20 character or create a new one already at level 20. I cannot for the life of me find the source of this, unfortunately, but I do distinctly remember reading it somewhere.
What I'm really curious about though, is whether you will need the Undrentide expansion in order to play this one? I didn't get Undrentide (although I likely will someday) but I'd really like to play Underdark. Any hope for me, or should I just wait until there's a "NWN Platinum" released with all the expansion packs including this one?