Narita to Osaka by Shinkansen

Hi All,

I'm planning to go to Japan around June this year and I have booked a flight that will arrive in Narita T2 at 16.25. Once arrived in Narita airport, I'm planning to go to Osaka by Shinkansen using JR Pass that I will buy beforehand. Assume that after landing I needed to go to immigration, then collect baggage, etc and finished at 18.00. Is it possible or efficient to go to Osaka straight away after that? How long does it take to activate my JR Pass at Narita airport? Also, how long does it take to get from Narita Airport to Shin-Osaka?

This will be my first trip to Japan, hence I really appreciate your advice.

Thanks.