Speeds are often reduced if the road is sub par or if there have been accidents on that bit of road.
Yes. The limits are low, but definitivly not _incredibly_ low.
I drove Oslo Airport -> Flåm -> Bergen -> Oslo Airport. Looks like E16 / 7 / 52 were the roads involved, 968km loop.
The motorways are mostly on the south-eastern part of Norway, where it's reasonably flat. There aren't that many of them, building infrastructure here is really hard.
[1]: https://www.nrk.no/hordaland/e16-bergen-voss-kara-til-_noreg...
I don't disagree that it's very difficult to build infrastructure! Every road must follow the contours of a fjord, or go over or through a mountain. I was very lucky to be able to drive the world's longest tunnel; I had read about it but honestly forgot about it until I made a left turn into a mountain and was perplexed as to how I could get to where I was going by driving into it.