Advice on Shinkansen between Tokyo and Kyoto

I will be spending three weeks in Japan at the end of March and beginning of April. It is my first trip and I am very excited travelling alone. I will spend the first few days in Tokyo. My hotel is close to Kuramae Station (near Asakusa).
On April 1st I am planning to take a Shinkansen to Kyoto. I would like to buy the ticket in advance because I fear that I won�et be able to get one due to the high amount of tourists during this time of the year.
My question to those of you experienced in Japan travel: Which of these options would you recommend?
1. Take the subway from Kuramae to Tokyo station, change to Shinkansen there.
2. Go to Shinagawa station from Kuramae and bord the Shinkansen there.
Please bear in mind I have never taken a bullet train before nor have I navigated a Japanese train station before. I am nervous about finding my way with a suitcase during (probably) morning rush hour.
Thank you for your advice!

Buy the ticket when you arrive at any JR station. The number of tourists is tiny when compared with the number of Japanese people taking the train, and with 10 shinkansen trains each hour, you will not have difficulty buying a ticket and getting a seat.
Train stations have good signage. If you can navigate an airport to get to Japan, you can navigate Tokyo station to catch a train.

As there is a direct metro line from Kuramata to Shinagawa I would take the train in Shinagawa

You can either buy the ticket with reserved seat a few days before at any JR station it just buy it at Shinagawa. You are traveling alone. So no problem. I personally would take an unreserved seat at Shinagawa so I can just hop on the next Nozomi coming through. Minimal waiting time.