Does this sound good for 14 day JR Pass?

We are staying first 4 days in Kyoto and will not activate pass until leaving to go to Osaka.
30th december - Kyoto to Osaka
1 Jan - Osaka to Fukuoka
2 Jan Fukuoka to Kumamoto - we will spend two days exploring near by areas such as Takachiho via hire car
4 Jan - Kumamoto to Hiroshima and Miyajima if time permits
5 Jan - Hiroshima to Tokyo for 4 days
9 Jan - Tokyo to Kusatsu Onsen to ski for 2 night
11 Jan - Return to Tokyo
12 Jan - Nikko day trip

so we will be using the JR Pass from the 30th December to the 12 of January.
Will it be really busy on trains that time and hard to reserve a seat?

Thanks!