I'm sure you will get a lot of answers.
First, its 12-13 hours in the air. I can't do coach that long, so someone else will nedd to tell you how bad it really is.
Narita is very safe. Do a search in the CO forum for Narita information. Many people in that forun did quite a few mileage runs. Plenty of hotels and things to walk to. The town is really only about a 10 minute train ride away.
Everything you ever wanted to know about Narita can be found here:
http://net.saipan.com/personal/mike_...ta/narita.html

Enjoy.
Ed