Simplest Way to Shoot a Holy Grail Time Lapse 

Thank you Scott, and I am happy see you again ! ;)

Fantastic

If you shoot in aperture priority, wouldn’t the time lapse speed up in night time as camera would slow down the shutter speed to maintain exposure?

Thanks Scott, I'm a long term photographer, but new to video. I just liked and subbed as I'm inspired to get good at doing this in some awesome locations. I shoot on Sony too - which looks pretty capable for this kind of thing, esp. now they added back interval shooting into firmware (it was missing when I first bought a Sony a7riii late 2018). I know I need to get out shoot, review, learn, adapt, shoot more etc as a good way to develop my skill. Currently I haven't done this yet, so it's still conceptual for me. I'm pretty sure that after I start doing practical shooting, rather than just reading about it, that things that are vital, vs just nice to do, will become a lot clearer. One query is the S&Q mode on Sony video (which I never yet experimented with), which you don't mention? Is this something one should effectively ignore or potentially embrace as well as or instead of shooting a series of stills? Clearly if following your tip on shooting raw, then it looks like stills is the way to go (since raw output in video frames isn't an option due to patent limits on Sony, unless capturing to a Ninja V on a separate drive). Currently I don't quite understand how 400+ stills are imported into edit software to create a video (say output to 24 or 30 FPS). For video it's hard to see much need for resolution beyond 4k (currently, albeit that may change in future) - which is way smaller than stills on just about any full frame Sony. So would appreciate any thoughts you may have on this/futureproofing. Sorry lots of questions.

I'm still shooting with my old 6D's (got four of them though one is dead) I use Magic Lantern and use the ETTR feature to ramp my settings and for me it works well! A USB-C battery coupler and a large Pulse width Power bank Lets me shoot milky way timelapse all night

Auto white balance, or set it manually? Im just want to make sure before i spend those 2 hrs and get home a lil disappointed lol

Ten seconds is wrong for lots of circumstances, one of them the field of view. If you use two cameras covering the same scene, one with your 100-400 at 400 and the other your 16-35 at 16mm, then this will become clear. Ideally, your exposures will b one half of the interval duration. This gives the 180 degree shutter filmmakers adore. If you are using the camera's meter, you should also set auto ISO. If you use an external intervalometer, consider exposure bracketting. With the internal intervalometer too, if it's supported. My cameras don't.