FCDO advice including information on permitted duration of stay and visas for Finland: https://www.gov.uk/foreign-travel-advice/finland
For information on the validity of RYA certificates abroad see Evidence of Competence Abroad.
Although there is no specific requirement for evidence of competence other than that stipulated by the vessel's flag state, if asked a valid ICC should be acceptable evidence of competence as Resolution 40 has been formally adopted by Finland.
EU member state (part of the customs territory of the EU (which includes territorial waters)). Further information is provided on the Entry & Exit Formalities page under Customs - EU Member States.
Part of the Schengen area.
Unless arriving from a country which is part of the Schengen area, you must arrive and depart through a port of entry and complete a customs declaration.
See holding tanks for information on the discharge of waste water.
It is a punishable offence to operate a boat whilst under the influence of alcohol or drugs.