Guides (in English):

UKKO Freelancer guide for immigrants

Guides (in Finnish):

Free.fi – Yrittäjä vai palkkatyössä?
UKKO – Aloitteleva freelancer – Älä tee näitä virheitä 
Vero – Guidelines by the tax authority: VAT liability of visual artists / Kuvataiteilijoiden arvonlisäverotuksesta

Freelancer´s taxation guides (in English):

General information on taxation of visual artists (Artists’ Association of Finland
Vero – Working for more than one employer
Vero – Tax treatment of artists’ and freelancers’ income
Vero – Tax return – the self-employed
Instructions for freelancers on filing the form 15