The cheapest (and easiest) way to get to Finland (aside from airplane), is to take the Viking Line (or Silja Line ferry from Sweden (Stockholm or Kapellskär). To get there by;
They have booked sunny weather, 20-25 degrees C, for the convention, so you'll not need anything warmer than a T-shirt. The polar bears usually emigrate North every year around the 20th of May, so you don't have to worry about them either. Look out for the reindeer, though, they tend to get a little aggressive if it's too warm...And don't forget the killer sparrows, they are small but extremely fast!!