Welcome to Helsinki! I think you will be able to enjoy yourself...
To get an understanding of how much wind we have here you can browse this archive http://ws.bonware.com/eps/e/archive/
. The top of the gusts are about equal to the wind on open water.
With a Formula you can get quite a number of days during the season, but also with smaller equipment like a Freestyle and a 6.0 sail (if 75 kg) you can typically sail 2-3 says a week. 50-60 days per season is not impossible if you have flexible working hours.
There is flat water and chop in Helsinki, but by driving some 1.5-3.5 hours you can sometimes score some pretty decent wave sailing.
You will need a 5/3 steamer with a rashguard underneath (and boots, hood, gloves) early in the season (april, may) and late in the season (September, October, November). In between it is warmer and a shortarm steamer is quite appropriate.