For the starscape photos, I used some variation of the 500 rule - effectively, the longest exposure you can get without trailing stars is the result of dividing 500 by your full-frame equivalent focal length. This was sufficient on my 5D Mark II, however when I went to the 32MP M6 Mark II, that number dropped to 400, due to the sheer amount of detail it captured. Now I'm using a 45MP R5C, I may reduce it even further.
The magic of this is really in the editing. Lightroom's contrast, vibrance and dehaze sliders are miracle workers for bringing out the colour and making things pop just a little more.
Best bit of gear you can bring to one of these shoots is whatever you need to be comfortable enough to be patient. Camp chair, a few beers and warm clothes make all the difference.
