Nagano & Shinkansen

Hello.

I will be traveling from Shinjuku to Nagano on 31 March (Sat mid-morning) and return back to Shinjuku on 1 April (Sun late afternoon).
Intend to take the normal JR train to Omiya (Saitama) from where I will catch the shinkansen train.

Is it advisable to make an advance reservation for the shinkansen or can I buy the tickets a day before when I arrive into Tokyo ?
I am concern that it is a weekend and whether the trains will be full.

Also, if I buy a ticket w/o a reserved seat, does it mean that I can take another shinkansen train if I miss the one that I was booked for ?
Advisable not to reserve a seat then ?

Understand that Nagano is famous for its miso.
Does anyone know of a very good miso shop in Nagano city centre where I can buy the paste to bring home ?

Thanks.

Is it advisable to make an advance reservation for the shinkansen or can I buy the tickets a day before when I arrive into Tokyo ?

It is personal preference. I always prefer to travel with a seat reservation. If you do not mind paying the small addition and have your trip fixed in advanced, then I recommend to make the seat reservations in advance.

There is a website that lets you make seat reservations for the Nagano Shinkansen, but there are restrictions until when and where you can pick up the tickets once you are in Japan. Alternatively, I think it is rather unlikely that the trains will be booked out more than a day in advance, and you could probably just make the reservations once you arrive in Japan.

Also, if I buy a ticket w/o a reserved seat, does it mean that I can take another shinkansen train if I miss the one that I was booked for ?

If you get a non-reserved seat, you do not book any specific train. You can get on any train during the ticket's period of validity. If you get a reserved ticket and miss the train, then you can ride any later train in the non-reserved section.

Thanks again Uji.