1. Yes, it is possible. Tickets might be sold out though, although that doesn't seem very likely at all, as Tavastia usually only sells out when big bands play.
2. See above.
3. Ask people how to get to Kamppi, or Tavastia. If someone doesn't know where Tavastia is, I doubt you will find a person who can't give you directions to Kamppi. It's maybe a 30min walk there from the seaport. Once in Kamppi, you can't miss the huge construction area. On the edge of it is Tavastia, opposite to the movie theatre.
4. Yes, but I can't name any off hand.