JR East Train

Hello,
I need to book train tickets for two on March 18, 2024 from Tokyo to Sakudaira Station 9:04 . Can I just buy tickets at Haneda Airport the day before when we land in Tokyo? Will there be a chance the train will be full? Do I need to go to the JR East desk at Haneda airport to purchase them? If I purchase them on JR East online, can I just go to a machine at Haneda airport to get the tickets? We are not buying a JR Rail passes.
Thank you!

Can I just buy tickets at Haneda Airport the day before when we land in Tokyo?

Yes. Or you could also buy them just before departure on the day.

Will there be a chance the train will be full?

The train has unreserved seats, so you will always be able to board it. March 18 is the last day of a long weekend, and the trains may be quite busy. In case you fail making seat reservations, you could ride the train in an unreserved car.

Do I need to go to the JR East desk at Haneda airport to purchase them?

No, you can also purchase them at any other JR ticket office or at ticket machines. Or you can use C cards and eShinkansen tickets instead of paper tickets.

If I purchase them on JR East online, can I just go to a machine at Haneda airport to get the tickets? We are not buying a JR Rail passes.

You can pick it up at the JR East counter. Not sure whether there is a JR ticket machine at Haneda. I doubt it.

Uji is right, and while you can buy those JR tickets at any JR counter throughout Japan, if you wish to buy it at Haneda Airport, you do need to walk to the only JR counter the airport has.

JR tickets can be bought at any JR station at any time their trains are stopping at that station. I wonder which area you're heading to from Haneda Airport. If there is a JR station near your hotel, you can buy your tickets there as well.

Correction: March 18 is not a holiday next year (I looked up the 2023 calendar by mistake). It will be a regular weekday in 2024. Not sure how busy it is, but I doubt it is super busy.

Thank you both for the great information. The closest train station to our hotel is Tokyo station. I think we will go the day before to buy the tickets. I�fm sending my husband and son by themselves for fly fishing in Ueno Village and I want to make sure they get the correct train tickets.
Thank you again!