There's one mistake that maybe not very many tourists make, but that could be fatal, and that is underestimating the danger of nature. The natural surroundings in much of Norway are very different from what most tourists are used to. The terrain is steep, there's often no guardrail even on maintained paths, usually no lights, and the weather can and does change very fast. Always pack a rain jacket for your hike,tell someone where you are going, and listen to local advice.
Bring rain gear. We were there for 12 days in June 2024. It rained every day. It didn’t stop us from doing multiple via ferratas but you want rain gear that works including pants.
Sister-in-law was a waitress in Norway for many years. She and the other waiters/waitresses expected tips from Americans. That being said, she also told me that she ignored her other customers when she had an American at a table and gave the American the best service because she expected a tip.