My itinerary

Hello there,

1.) Travel to Hokkaido, Tokyo, Osaka can cost quite a bit and you can make very good savings compared to purchasing normal tickets. I recommend using a 14 day JR Pass, as you'll be traveling quite a lot and this way you have more time to visit each place/city.

2.) There are no night trains going from Tokyo - Sapporo covered by the JR Pass, you can use the Shinkansen instead during the day.

3.) Yes, you can make all the seat reservations you want at the time when you exchange the JR Pass. Its also fine to do so later.

4.) The JR Pass is counted in consecutive days.

Hope this helps,
Daniel