What is the local currency?
In currency in Finland is the Euro.
Should I change money before I go?
Not necessarily. You will be able to use your credit and debit cards in 99% of all places.
How much should I budget per day for extras?
On day 1 and 3 in Helsinki roughly 50-100 euros. Day 2 in Nuuksio National Park you won’t need or be able to spend any money.
Is it customary to tip?
If you are really happy with the service then do tip, but remember that Finns do not expect you to do so. It’s always a happy incident when it happens.