you can narita express round trip and the tokyo metro system is superb, but there's no elite entry to nrt so keep the 2 hrs buffer before departure. the security/immigration lines can run long. united's lounge at nrt is one of their best. probably due to the high standards set by asian lounges.

this is a guesstimate please check schedules but arrival departure and express train inclusive you have about 2 hours of sightseeing and possibly cheap world class sushi at tsukuji market.

lastly do not count on wifi or cell coverage. japan is proprietary and you'll need a japanese plan in most if not all cases. plan your excursion to the exact details to avoid getting lost and not having your google maps in hand.