Like someone mentioned, that focal range jump is a bigger deal than it looks on paper, but I have to politely disagree with the crowd saying f4 is garbage for low light. In my experience, people get way too caught up in specs instead of looking at how modern cameras actually perform. Your A7IV has incredible high ISO capabilities, so shooting at f4 in Tokyo is honestly not going to be the disaster people claim. My methodical approach to this would be prioritizing the 20mm wide end for your landscapes. The Sony FE 20-70mm F4 G is extremely sharp and much easier on the neck during a long day of hiking. If you are truly worried about the night street stuff, just use your leftover budget to grab a Sony FE 35mm f1.8 for when the sun goes down. It is tiny, fast, and the whole kit still stays under your $1200 limit. Better to have a light zoom and a fast prime than one massive brick that makes you miserable.

Ive been through this exact cycle more times than I care to admit. Over the years ive tried the heavy setup and the one lens approach. That back pain is no joke. In my experience, the jump from 28mm to 20mm is way more significant than people think when youre standing in a narrow alley. I used to worry a lot about having a fast aperture for night shots, but after a few trips I realized that bumping the ISO on these newer mirrorless bodies is basically fine for most street stuff. I eventually swapped my heavy glass for something lighter with a wider range. Ive found that the extra width at the bottom end is way more useful for landscapes than having that extra stop of light. My current setup stays on the camera 95% of the time and my back feels way better.