For weather, try a search comparing to your home area. I was near Tokyo with the US Navy for couple of years and didn't think it that bad. But from California and we were back and forth to the Philippines, Hong Kong, Singapore, etc., so had warmer,too.
Google Street View, YouTube and Vlogs on touring and photography or videoing Japan can show spots that interest and give views of some of your destinations that could offer some insight. Along with the different preferences and experiences here.
Is there something wrong with the 28-70/2? I mean, you did spend all that money on a day to night zoom for convenience, right? And it's only about 180 grams more than the 50 alone. I know 28 isn't 24, but I think you'd be surprised how easy it is to make 28 work in situations where you'd otherwise want the 24.
I love my primes, but, if it were a matter of my health, I were determined to do it with a FF, and I already owned that lens, then it and an a1II would be my choice. But then I think of this...
a6700, Sigma 10-18/2.8 (favorite lens in Tokyo), Zony 24/1.8 (my fav focal length on the crop, but if you're more a 50mm shooter, the Touit 32/1.8's a better choice), and Tamron 35-100/2.8 (fantastic lens for the crop with a relatively nice size and weight, plus works well with a Kenko Pro AC1 No. 3 diopter, so a dedicated closer focuser isn't necessary for vacation pics) packs for about 1600 grams with extra battery, cards, and filter.
a1II, Sony 24/1.4, 50/1.2, and 100/2.8GM mac, I'd be at about 2700g with an extra battery and cards. That's without considering the second camera, extenders, or the bigger bag necessary for this kit.
I could work with either, and I know there are sacrifices made with the slower kit, but, if I needed to baby my health, I'd go APSC.
