I have friends who have autofocus lenses and have a difficult time achieving good focus because it's difficult/impossible for the AF mechanism to focus on stars and because many autofocus lenses typically focus past infinity, making it very hard to focus manually on screens that weren't made for that.

I've found with manual focus SLR and rangefinder lenses that the infinity stop works very well for tracked stars and star trails.

A plastic cup that fits over the lens and is either black or lined with black material is a great aid for blocking plane and satellite trails.

Also be sure that you don't have any leaks from an electronic viewfinder display onto the film with long exposures. I have one SLR that does that, but it has a mechanical B setting, so I can use it, but have to pull the batteries first. Many electronic shutters run the batteries down very quickly with time exposures. My DSLR using friends have to bring an outboard power supply for their cameras.

Some lenses are best stopped down 1/2 to a full stop for best image quality, especially at the corners. Test.

I'm not a real Nikon user, so I can't speak to specific appropriate bodies.

Lee