16-35 f/2.8L III for astro?

[Frodo]

In response to the OP's question 3, the 16-35 F2.8 III and the 24-70 F2.8 II are both very good lenses, but they are both heavy and there is a lot of overlap. So, one question might be how important is it to close the gap between 35 and 70, figuring in the possibility of zooming with your feet, stitching and cropping.

Or the overlap between 14 and 24?
I remain happy with my Samyang 14/2.8, especially because of the lack of coma and its pretty sharp wide open. Photoshop corrections remove distortion and vignetting (with a little extra noise).
Looking at your shooting stats and your current kit, I'd take the 14/2.8 and 24-105/4 hiking. I do. This covers most things for modest weight.
This option is probably the lightest weight. And the cheapest!