Just to prepare you for reality, Lake Como, Luzern and the Jungfrau Region are all going to have crowds. Not once you get off the beaten path on hikes, but in the train stations, main streets and popular attractions, there will definitely be crowds. September is slightly better than July, but even up through middle of September there will be lines out the door for the cable car up to Murren on a nice day and standing room only on the train to Grindelwald. I've done the walk from Mannlichen to Kleine Scheidegg many times. The first time I walked it in 2010, we had the trail practically to ourselves. Summer 2025, I walked it with hundreds of people. You basically all walk in a line and if you want to pass people, others will have to stop and push to the side, as it's a fairly thin trail. The cable car up to the Schilthorn will be filled to capacity. First Bachalpsee will have many people. If you want less crowds, you have to pick spots that aren't regularly coming up on forums & social media.
Aside from the crowds, to answer your question, you’d want 5 nights to accomplish your list. Wengen is a good centralized base. Prioritize a southern facing balcony and don’t get too far downhill from the train station.
1 day - Wengen > Männlichen > Kleine Scheidegg > Wengen
1 day - Wengen > Lauterbrunnen > Stechelberg > Schilthorn > Birg Thrill Walk > Murren > walk down to Gimmelwald > Stechelberg > Lauterbrunnen > Murren
1 day - Wengen > Lauterbrunnen > walk or bus the valley in the morning + stop at Trummelbach Falls > Murren > Allmendhubel > Northface hike counterclockwise in the afternoon back to Murren > Grutschalp > Lauterbrunnen > Wengen
1 day - Wengen > Grindelwald (via Mannlichen or Zweilutchinen) > Grindelwald First > Bachalpsee > Grindelwald > Wengen