Mytrims is a very good place to find info of the spots in Finland.
Equipment: winds in Finland are mostly light. So, if you want the get the most out of your summer, get formula equipment. But sometimes it can get windy, so you might also need smaller equipment. We sometimes get waves also, in Hanko and Pori.
You will need a winter wetsuit here! Then you can start to windsurf when the ice melts (April-May probably).
If you want, i can email you more info, I live in Helsinki too.
My email is timi.hell (a) hotmail.com