I’ve written a blog post about the basics last year:
https://blog.pixelbook.org/2018/09/night-photography-image-processing-using-darktable/
Replace base curve with filmic now 
About taking the pictures: You camera for sure has ISO in-variance, find out when the ISO ramp changes for your camera and then shoot with that ISO. I take night pictures as ISO640, it switches to a different pitch at that ISO.