I don't know any exact numbers of the windspeed since I'm not a sailing or windsurfing much.
There are plenty of sailingboats and some windsurfers though so there is definately windy...And it's more windy than a protected lake since it's the sea whit lot's of space

The archepelago area has both larger, open water areas as well as smaller water areas scattered with¨islands.
Mostly the shores of the islands are 95% rocky/cliffs, but there are also some sand beaches.
(Make a search for archepelago + Finland in Google to see some nice pictures, I think there are totally >5000 islands and rocks out there, it's truly beautiful nature.)

The idea of catamran sailing here would be to explore and go for weekend trips as much as daysailing...No competitive racing, but speed is always a high priority, otherwise I could as well buy a comfortable "normal" sailingboat.