This is a big question, like how long is a piece of string.
Thee easy part first:
Winter Tires? Yes!
Especially spring/winter is tricky with potentially positive temperatures in the day, melting snow and causing water in the road and freezing in the night.
Change tires around Stockholm is a good idea. you might even borrow/rent wheels from someone. Such as us…
If you are planning on exploring roads with lot’s of snow you might even consider snow chains.
For winter camping, the first thing that comes to mind is heating. How do you heat it?
Then look over engine coolant and screen wash fluid
door locks, special cold weather oil/defreezing fluid. Available in most fuel stations here
I especially hate the fuel filler lock, so for winter I use a non-locking fuel filler cap. Others have success in unlocking even in cold weather, using the lock fluids as above.
This is a starting point.