Time lapses across the day to night transition are not a simple thing to do. Fred (Bassnut) built a complete system to control his camera to adjust aperture and exposure to accomplish this.
I suggest you simplify your initial attempts till you get the hang of timelapses before launching into the full transition through large light changes.
That's enough of a challenge on its own.
Aperture, exposure and ISO are all a bit of a trade off. Longer exposure and higher ISO increase noise, but capture more light. Big aperture captures more light but at the expense of DOF.
For star trails with not much foreground (or the foreground is quite well away) you can use a bigger aperture (smaller number). If you have a close foreground object you also want to capture as well as the stars, you will need a high aperture number (smaller aperture) for the DOF.
If there's action you want to stop in each frame, that will determine your exposure. depending on your lens FL, you might be limited to 15s or 30s before the stars noticably elongate for example.
Then your final trade off will be the ISO. Try to get enough detail without unwanted noise.
Its all trade offs... a bit of a balancing act.
Does that help?
Al.