Thank you. I want to shoot some but what I've seen on the internet is quite variable. A good starting point seems to be full frame, ISO 800, F 2.8, 15 sec. From here higher ISO and shorter exposure times.
Just in case the sky is clear enough for astrophotography I'll probably get the Nikon D750 with Samyang 14 2.8 and Nikon 24 1.8G specifically for this, I should have enough room.
Even on APS-C I doubt I'll lose much at ISO 1600, after all I don't expect that much detail in a night shot.