Nice start and good luck going forward. I dabbled in astrophotography and really enjoyed it, but when I lived in Illinois it would have required me to drive hours to get to someplace dark. The darkness will greatly impact your results. I am including one photo from a sky not dark enough and one from Arches (a designated dark sky park), and you can really see the difference.
I intend to eventually purchase the lens you are using for astrophotography, it's a great choice. I am no expert, but when researching I saw that you should be able to shoot that lens for 25 seconds at 1.8 without any appreciable smearing of the stars. I wonder what that would look like. I don't know how dark it is there, so I don't know what ISO to suggest, probably something between 3200 and 6400. I know how you process the image can greatly impact things as well, I did some research to figure that out and again am no expert.
Nikon D850, Sigma 14mm, f2/2, 25 secs, ISO 1600 25 minutes from home at that time, farm country, barn, fireflies and corn
Nikon D850, Sigma 14mm, f2, 25 secs, ISO 2000 Arches National Park, painted the structures with a flashlight, which is now prohibited there