Here is my itineraries:
12/24 - arrive Narita Airport and plan on taking the limousine bus to the hotel at Shinjuku
12/26 - take the Shinkansen to Arima Onsen and spent two nights. Might go to Osaka and Kobe for day trips.
12/28 - back to Tokyo for 2 nights.
Should I get the JR pass or buy as we go?