The Japan Rail Pass will make sense if your planned trip to Osaka is within 7 calendar days. The round trip fare to Osaka is about equal to the price of the 7 day Japan Raill Pass, plus you can use the pass to take other JR trains.

Since you mentioned staying Shinagawa Prince, I assume you will not immediately travel to Osaka as you land on the 23rd. I would get the 7 day Japan Rail Pass to cover the travels on 24th to 30th, which should include the round trip to Osaka and the Narita Express outbound trip on the 30th to NRT. For the travel on the 23rd, I would get the Suica and N'EX deal. If you have lots of luggages, you may opt for limo bus instead.