What obligations arise for the company after it is "opened" in Finland, are some kind of tax declarations required?

It is obligatory to submit tax reports and you can do it via the Internet. In case, the company does not have any activities, but it is registered as a taxpayer in Finland, the company will not pay taxes for its activity, but reports should be submitted anyway. If your company is officially situated in Finland, then you pay only VAT. On the territory of Finland any company can be registered as VAT payer.