Reservations on Shinkansen

Hi all!

I will be travelling to Japan from 17 April to 26 April.
I'm going from Tokyo - Shizuoka - Kyoto - Hiroshima - Tokyo (crazy for 10 days I know)
But my problem is I've actually planned all my shinkansen timings at around 8am plus for all the locations and I just totally forgot about peak hour!
So I was wondering,

1) Can I make reservations for all the rides in advance? I've read somewhere that reservations are only accepted on JR East line. (I've bought my JR Pass btw!)
2) Should I plan my Shinkansen timing to avoid the peak hour (after 0930am)?
3) Does the peak hour apply to all prefectures? I know Tokyo is insanely crowded in the mornings, but is it the same in Shizuoka, Kyoto, and Hiroshima during 7am to 9am?

Sorry I have so many questions! Would really appreciate some help on this!

Thanks!
Kai Ting