Which Pass and when to activate

Hello!

I hope you don't mind a quick questions. I am visiting Japan next month and plan the following. I would love your opinion/advice on whether to adjust the plan or when to activate the pass:

Arrive Narita
3 nights in Tokyo
3 nights Osaka
2 nights Kyoto
1 night Nagano/Jigokudani
1 night Tokyo
Depart Narita

When would be best to activate the 7 day pass or would we still save more by purchasing a 14 day pass so we can use it on the trains to and from the airport and on the network within Tokyo?

Thanks so much for your help.

Chris