Will I Need It AND How Will I Know?

My 2 friends and I are visiting Japan in 2 months! We will be staying for 2 weeks and I am trying to be as organized as possible. I know we will be taking the subway a lot, but I am very confused about when the JR Pass comes in. These are the cities/ districts/prefectures we will be traveling.

Haneda Airport -> Yahiro Station
Yahiro Station -> Tokyo (Shibuya, Shinjuku, Kabuchio)
Yokohama and other parts of the Kanagawa Prefecture for a couple of days with no overnight stays.
We will be going between Kyoto and Osaka for 3 days and return to Tokyo.

Will I need the JR Pass for this Itinerary or is it best to buy tickets as we go?