Should I get Jr pass for my itinerary?

I am planning a trip to Japan in December as follow:

Day 1 : arrive at Tokyo
Day 2: Tokyo
Day 3: Tokyo to Osaka (include a day trip to Kobe)
Day4-Day6: Osaka
Day 7: Osaka to Kyoto
Day 8: Kyoto-Nara-Kyoto
Day 9: Kyoto to Nagoya
Day 10: Nagoya
Day 11: Nagoya to Tokyo
Day 12 to Day 16: Tokyo

Should I get a 7 day pass or 14 day pass? Which is more worthwhile?

If I start using the JR pass from Day 3 for the trip from Tokyo to Osaka, the 7 day pass will expire before I reach Tokyo. Should I skip Nagoya so that I can make use of the 7 day pass to go back to Tokyo?

Thank you.