7-day or 14-day pass?

Hi,

I will be traveling to Japan my first time at the end of August 2017. I will land in Tokyo. I plan to take a train to Kyoto and stay for 5 days, and take occasional day trips to Osaka during the 5 days. We will then train back to Tokyo on the 7th day and then head back to Tokyo airport on the 10th day. Would you recommend a 7-day or 14-day pass? Is a JR pass worth it? Are there any better passes that fit better for my itinerary?

Also, when do the trains end? Will I be able to train to Kyoto late at night from the Tokyo airport? I land around 7:40pm. After going through customs and getting my JR pass, it could possibly be 9PM. Please help! Thanks!