I can't answer most of it, but here are my comments.
I know you probably think that this will be your only trip to Norway. However, cruising to Flåm and Geiranger will be very limited after 2025. The same is not true for Olden and Loen. So that might influence your decision.
I went in June. The weather at Geiranger and the sail-in was lousy, foggy and damp or rainy. Despite that I enjoyed the sail-in from the ungodly hour of about 5 am. However, when we went to Flydalsjuvet there was very little visibility. At the top of Mount Dalsnibba there was absolutely none. Flåm, on the other hand, was a glorious day, and I very much enjoyed the Næroyfjord cruise in lovely sunshine. The 2 areas looked totally different because the skies were different.
I didn't go to Olden, so can't comment on that.