I'm by no means an expert, but IIRC you want to shoot at low ISO. Long exposure already adds noise, you dont want to add high ISO noise. You were right about the timer, also add mirror lockup.
Getting the exposure right for both the sky and the nearby lights is difficult, try to stay away from any artificial light sources.
What do you mean by "set to infinity and let the camera autofocus"? Did you focus manually or auto focus? The few times I played around with this, the camera could not auto focus (too much light pollution and stars not bright enough)

Arnt