Hi Leggy, hope you manage to read this somewhere. I'm afraid that Klonkku hasn't been around on this site for a long time.
But, a piece of advice regarding getting to the train station. It's maybe most clear to take the shuttle bus back to the airport, from where you can take one of the regional bus lines to Helsinki: 615 (recommended, it's an express line), 615T, 415, or 451, or the Finnair express bus, which is more expensive though. For all of them, the other end of the line is right next to the Central Railway Station where your train will depart.
And, let us know when you get to Joensuu.