10 day trip during golden week, 7 or 14 day JR pass

Hi!
I am planning a 10 day trip during golden week and am debating a seven day or 14 day JR pass. Since it is golden week I am very nervous about the trains being busy and assume I should reserve train tickets in advance. Is it better to get a 14 day pass and reserve all my tickets on day 1 at the Narita airport? Or should I get a 7 day pass and activate it on day 4? Where can I activate the pass aside from the airport? Also what route should I take on day 6 from Tokyo to visit a Hakone onsen then go to Kyoto?

1-arrive Narita
2-5- Tokyo
6-Visit onsen in Hakone then leave for Kyoto
7-9-Kyoto
10-Kyoto back to Narita

Thank you!!
Faith