Five days Narita-Tokyo-Kyoto: Do we need JR Pass or can we book separate tickets?

Hi, we are going to visit Japan between 19-23 December. Arriving in Narita on the 19, we want to go directly by train (N'ex and Shinkansen) to Kyoto, stay in Kyoto 19-21, back by Shinkansen to Tokyo, stay there 21-23 Dec then leave through Narita.
I calculated it is not economical to purchase the JR Pass but buy separate tickets, but is it possible to do so?
Can we book the meet and greet service in Narita without booking the JR Pass itself, and then get help in booking the train tickets upon arrival in Narita? (We are afraid the flight might be delayed so if we book tickets in advance, we might miss the trains).
Thanks in advance for your answers!