Question about pass vs tickets

Hi,
I will be visiting Japan in October, and the plan is to take the train from Narita airport to Shinjuku Area. We will also be taking trains from Tokyo to Kyoto, Kyoto to Nara and back then from Kyoto to Osaka during this trip.
When purchasing a rail pass, would the 7 days be a consecutive 7 days regardless of if you take a train or not? Or only for the days you use JR train services?

Also, if i decide to purchase reserved tickets online, is there a possibility of changing departure times? I'm not sure how long it will take us to get through customs at Narita, so i'm hesitant to pick a departure time. If i am able to change the ticket, is there a maximum amount of time changes i can make?

Any help is greatly appreciated. Thank you in advance.