Reserve seats

Hi. I will be buying a 7 Day JR Pass. I understand that I can activate it at the airport at arrival and select a later date to start using it. I arrive on 23rd Dec. Plan to start using the pass on 25rd Dec.
- Can I reserve seats before 25th Dec?

23rd and 24th Dec in Tokyo/Shinjuku
25th Dec Tokyo/Shinjuku to Kanazawa
27th Dec Kanazawa to Osaka
30th Dec Osaka to Tokyo
then in Tokyo and its wider area till 1st or 2nd Jan
What is the best part of my journey to use the 7 day pass?
Any suggestion of changes in configuration is welcome.
Thank you!