about taxes while studying/having own buisness

[gloomy2011]

I have been thinking about how to earn some money in Finland while studying/doing part time job and I thought about selling something via online auction site. I think my earnings would be quite small under 8500€ and I was wondering what kind of taxing/expenses would this include? I read on the forum, that I could keep the income as extra without starting a toiminimi and just add it to my income salary, but I would like to have toiminimi in case it starts out well and would be worth continuing in the future as well.