I travel a lot for business and have really slimmed down my travel kit in recent years. I don’t tend to be a wide shooter, and for travel a 50 Lux ASPH is my primary Leica lens on M10 or M240, with a 35 on a second body or in my pocket, and that’s all. I also spent 3 weeks in Italy recently with just a Nikon DF and a 50+24 AIS combo and was very happy with just those two lenses for architecture, scenics, narrow street shots, etc.
So if I had your gear and was planning this trip, I’d be perfectly content with the 50 Lux on the M240 and the Q for street/wider shots/backup body. But if I owned the 21 as you do, perhaps I’d add that for those wider architecture/scenic shots beyond 28.
I just recently passed through Tokyo airport with a layover, but alas didn’t feel I quite had time to go out and explore due to a tight schedule. Should have added a couple days there. Enjoy your trip!
The 21mm f1.8 Voigtlander is really a brilliant lens. The 40mm f1.2 is also excellent and the 15mm is great for those close distance or to capture wide landscapes. I wish I had those same or similar lenses in the Leica brand, preferably Summilux, but I don't. The 50mm 'Lux is fabulous but I'm thinking it will be too long for crowded, small places. Perhaps the 40mm might be too long as well, but I'll take it anyway. The 15mm focal length is a no brainer. Perhaps I'll throw the 50mm 'Lux and the 28mm Elmarit. in my carry-on just in case....