HAYABUSA 21 dep time is 12:46, 12 mins total,http://www.eki-net.com/pc/jreast-shinkansen-reservation/english/wb/com...
maybe arr No.13, dep 17 track, fr 3F down to 2F up to 3F,
no need ticket gate out/re-enter at 2F, under 4 mins usual very easy, open stn maps.https://postimg.cc/fJ17fkTVhttps://www.jreast.co.jp/e/stations/e350.html
In the first map is not written elevators(lifts) into right(north) side blue circle,
but second JR-EAST official map is written it, no worry.
Both Shinkansen Car No.1 are map left(south, Tokyo) side.
Omiya is not end stn of Max Tanigawa,
so you should move close to the door 1 minute before arrival, be careful stairway down.
This Max means "Multi Amenity Express" but now just using
as JR-East's E4 series double-decker cars type shinkansen train name enough.https://en.wikipedia.org/wiki/E4_Series_Shinkansen
And, Idk which stn you to go w/Hayabusa, in JR-East's Shinkansen bento(lunchbox)
and hot coffee sales(wagon service items) was finished this summer,https://pbs.twimg.com/media/D-zSbPsVAAAL_hj.jpg:large
but 3 stores(NEWDAYS and EkibenYa) in the middle of Hayabusa dep platform(island).
NEWDAYS is JR-East group company's convenience store name, also calling smaller one KIOSK.
EkibenYa is one of old train restaurant service campany's store brand name,
so,you should buy something there, some ekiben that heats when pull the string is famous. https://blogimg.goo.ne.jp/user_image/3a/d7/3bbe336a4cc7910ac7af8b6d115...https://www.nre.co.jp/Portals/0/ekiben/ekibenyaomiyaeki/shop/DSC_0764....https://www.nre.co.jp/Portals/0/ekiben/DSC_0015.JPGhttps://youtu.be/AdKqF6SE2Bg
It doesn't matter if booked Grand Class.https://www.jreast.co.jp/e/routemaps/tohokushinkansen.htmlhttps://www.jreast.co.jp/granclass/en/
This is no important, just one of fun if taking Shinkansen first time,
try coin balancing challenge and real time speed check w/cellphone GPS apps.https://youtu.be/ra2HenPYJYE https://youtu.be/4qnfZ2x3xX8