First time poster, long time lurker.

If you live close to the Canadian border (or go there frequently) NEXUS would be your best deal as it's $50 for 5 years (and includes Global Entry) v $100 for Global Entry alone.

You can sign up for Global Entry even if you have never done any international travel. In fact, it's one thing CBP has been complaining about, that people are signing up for Global Entry just to get PreCheck. Once you do have Global Entry, you can enter your PASSID ("Trusted Traveler" ID) into your frequent flyer accounts and use PreCheck on any airline that offers it.

To answer your question, yes. You do need a passport for Global Entry as it is intended for international travelers.