I've ridden most of the northern bit, and the stretch south-west from Inari twice. One of my favourite roads.
Inari is the last place for shops and restaurants for about 200km, so the place to stock up
Reindeer pizza in Inari
The first place marked on the map after Inari is Pokka,
There are signs every 10km telling you how far it is, and when you get there there is a small cafe (coffee and cake) petrol pumps and very little else (a handful of houses spread among the trees, that's it).
Streetview: village centre of PokkaOh yes, it's got a sign saying it recorded Finland's lowest temperature.
Just south of Pokka the tarmac runs out, but it's perfectly rideable. Though perhaps not so in darkness.