What time does the train station open?

I'm going to Japan for the first time alone and I'll use JR Pass. I'm planning a trip and come up with a few questions.

I'll take shinkansen Hikari 501 from Shinagawa station to Shin-osaka very early in the morning (6.34AM)

1. What time does the Shinagawa station open?

2. Will I be able to buy bento that early time to eat on the train as I won't be able to have breakfast at the hotel?

And the train will arrive at Shin-osaka at 9.30 AM, and then I have to take another train to Hiroshima. I plan to take Sakura 551 which departs Shin-Osaka station at 09.59AM. I want to be in Hiroshima before noon.

3. Will I be able to catch Sakura 551 in time? Is it difficult to find the platform?

4. I'm confused. is "track" shown in hyperdia the same as "platform"?

Thanks so much in advance for your answer.

What time does the Shinagawa station open?

I am not sure whether it ever fully closes. The ticket gates will open before 5am when the first trains start running.

Will I be able to buy bento that early time to eat on the train as I won't be able to have breakfast at the hotel?

I think that some of the shops inside the station will be open from around 6am. Additionally, I assume that there are multiple 24-hour convenience stores around the station that provide good breakfasts.

3. Will I be able to catch Sakura 551 in time? Is it difficult to find the platform?

You will have ample of time. The transfer takes less than 5 minutes. The station is full of bilingual signs, and it will be very easy to find the platform.

According the the current timetable, Hikari 501 arrives at Shin-Osaka on track 22, and Sakura 551 departs from track 20.

I'm confused. is "track" shown in hyperdia the same as "platform"?

Yes.

Will I be able to catch Sakura 551 in time? Is it difficult to find the platform?

It can be easier if you know the way in advance. I suppose you will have enough time.
If your Shinkansen train departs at Track 20 in Shin-Osaka Station,
then one thing to note is that there is no direct route connecting Track 20 platform on the 4th floor and the Shinkansen concourse on the 3rd floor; you can change elevators on the middle floor.
# Track 22 --[common elevator]-- middle floor --[common elevator]-- concourse
# Track 20 --[upper elevator]-- middle floor -- [common elevator]-- concourse
So, in order to make this transfer from Track 22 to Track 20, you can either
take the common elevator down to the middle floor then take the upper elevator, or,
take the common elevator down to the concourse, take it up to the middle floor then take the upper elevator.

I'm confused. is "track" shown in hyperdia the same as "platform"?

Trains run on tracks, not on platforms. A platform is a construction used by passengers to get on / off a train.
One platform is designed for one or two tracks.
Some people use "platform" with a number to mean a certain track, but I personally don't.

What time does the Shinagawa station open?

Will you begin this trip from Shinagawa? Or will you make a transfer in Shinagawa?
There are three Shinagawa Stations.
# Beginning from Shinagawa Station on Shinkansen
In Shinagawa Station of JR-Central (= the operator of Tokaido Shinkansen), ticket counters open around 5:30 am; the north and the south Shinkansen concourses are separated.
# Making a transfer from JR-East
In Shinagawa Station of JR-East, the north ticket gate can be used for the earliest trains, but you will not have to use it; there are two pathways connecting JR-East and the two JR-Central Shinkansen concourses, each with a transfer gate in between.
# Making a transfer from Keikyu
Takanawa exits of Shinagawa Stations of Keikyu and JR-East are located close. From Keikyu you can walk on a pathway over JR-East lines to the entrance of JR-Central and then pass through a gate to either north or south Shinkansen concourse.

Will I be able to buy bento that early time to eat on the train as I won't be able to have breakfast at the hotel?

You are highly likely to get food (though it may be not a bento) and soft drink.
Near each of Takanawa and Konan entrances, there is at least one 24-hour shop of convenience store chains.
In each of the north and the south Shinkansen concourses, at least one food-selling shop opens around 6 am.
In the north Shinkansen concourse there are a Bellmart shop (opening at 6:00), bento shops, a kiosk and two Starbucks Coffee shops (one opening at 6:00).

dear Panar,

I understand how u feel n am posting to reassure you that you WILL be able to transfer frm 9.30am train to the 9.59am departing train in time.

The 2nd poster was trying to gv u specific information but i can understand that it sounds a bit frightening - with all d go up n down escalators directions.

I dont speak or write Japanese n was fine getting my train transfers.

Just dont linger n go look for the next train platform/track as soon as u get off the first one. I dont bother to try running around looking by myself and immediately ASK the nearest train station staff - usually at some exit/entrance turnstiles. They will have a uniform on and mostly speak some English AND will give you the correct directions. Passersby may not gv u the correct info although trying to help.

It is easier than it sounds as written by the above poster. So dont worry.

P/s not everyone wearing a uniform is station staff - once i asked a pilot on his uniform!! Haha