For most PhD positions in Finland, the gross salary is EUR 2000. How much tax is charged on this? Are there any other deductions? Basically, is the in hand amount sufficient for living in Finland for a non-EU/EEA student?

I have googled the subject but long time ago. I think the salary is 2000 net not gross. If so, it should be ok even Finland is more expenses than west Europe.
In terms of salaries in Europe for PhD, I would summarise as follows:
UK: £1100- £1300 monthly net + exemption from council tax
Germany: Scholarship 1000€-1300€ net. RA: 1500€-2500€ net. All PhD students get reduced transport tickets
Netherlands and Belgium: around 1400€ net
Finland: around 2000€ net
Sweden: 2000€ - 2500€
Switzerland: 3000 CHF -4000 CHF