You are on the right track. I like to take night shots and have made several outings to try and catch some meteors. A couple of months ago I went to Death Valley with some friends during the Lyrids. I set the camera up and told it to take pictures for six hours.
I was looking for pinpoint stars with a meteor or two so I kept within the rule of 600. I didn't have any luck on the meteors so the next morning I played around with making a time-lapse. It was OK but I was only using iMovie and it wouldn't let me set the frames to anything faster than .1 sec and it was rather slow.
When I got home I looked up stacking software and found StarStaX as mentioned above. I was shooting and RAW + JPG and StarStaX processed the 720 JPGs in about five minutes right off of the camera output and resulted in this image.
This was taken with a Nikon D7000 and a Tokina 11-16mm lens. The zoom was set to 11mm so the rule of 600 would dictate a maximum exposure of 600 / (11 * 1.5) = 36 seconds. Using the built in intervalometer I setup the camera to take one 25 second exposure ever 30 seconds. I chose 30 seconds so that time calculations would be easier. The 25 second exposure was because the camera would skip shots when I set it to 30/30.
I was shooting at ISO 800, f2.8 and the corners wound up rather soft. What is amazing is that it was so calm that night that the trees didn't get completely blurred. You can see a few airplanes in the shot and I later removed them from the individual frames. Even with the settings I used you can see gaps in some of the trails. The trees are lit by the campfire in about 100 of the images.
Some notes:
The rule of 600 gives you a good baseline for shooting a pinpoint star. The closer to that limit the more your stars will start to elongate.
Stacking photos helps to remove noise from the final image.
If going for star trails see how long you can push your camera before the image starts to get objectionable. Then minimize the time between shots. For example if you can shoot a good quality image at three minutes and then pause a second between shots for the camera to process it you will get a much more solid trail.
Use your ISO and aperture to control how many stars you get in the final image. I think my above photo might have too many trails to the point that it gets distracting. Had I reduced my ISO I would have lost the fainter stars. This would also have changed the play of the campfire on the trees. I don't know if this would have been good or bad - just something I would have had to try. I could have also reduced my aperture to get a sharper image in the corners.
Experiment and have fun!
Here is what an individual frame from the above picture looks like:
At the same time I was using a D60 to take a 30 minute exposure:
Notice the sensor noise in the corners and the change in the color of the sky. This is what I meant when I said to push the exposure time to just before the point the image becomes unacceptable.
This also points to another issue with star trails - the D7000 was tied up for six hours. Having some older bodies (a D60 and two D70s) lets me keep occupied while the camera doing its thing. Eventually I just went to bed and let the camera click away.
