I got a reply!

Almost immediately. Very surprising.

マランダー　リーさん
連絡ありがとうございます！
オーケストラの参加もちろんＯｋです。
歓迎します！
さっそく明日、練習があります。
ａｍ10:00から
場所は、龍郷町りゅうゆう館です。
また今度、英語の話せる人からメールを送ってもらいます。
奄美オーケストラ

No translation accompanied the reply, but here's what I could piece together using what little I know of Japanese, with the help of Google Translate. (It's probably inaccurate.)

"Maranda Li-san, thank you for contacting us. Yes, it's ok for you to join the orchestra. Welcome! There is rehearsal right away tomorrow starting at 10 am at Ryuuyuu Hall in the town of Tatsugo. Soon we'll have someone who speaks English send another message. - Amami Orchestra"

In the next few exchanges (which remained in Japanese), they offered to let me borrow a beginner's cello until I could visit the string shop on the mainland to rent my own instrument.

I also asked about their upcoming program, which features movements 3 and 4 of Beethoven's ninth symphony (!!) as well as traditional island songs, anime theme, and other fun things. They rehearse Sunday afternoons, from 1:30 to 4:30 pm, and are based in the main city on the northern half of the island, 26 miles from Setouchi. Still, thanks to winding island roads and the slow pace of island life, it takes 50 minutes by car or about an hour by bus to reach it.

This will be a great opportunity to get to know locals while doing engaging in a shared activity; after all, music is the universal language. Grassroots internationalization at its finest.

My first correspondence in Japanese!

I must be feeling adventurous tonight. The Amami Oshima orchestra's website has a "contact us" button, so I composed a simple message to introduce myself and voice my interest in joining them in both Japanese and English:

初めまして、

マランダー・リーです、瀬戸内町の新しいJETです。七月二十七日から始めて、古仁屋高校に英語を教えます。よろしくお願いします。

アメリカから来ました、大学で私の専攻は音楽です、チエロを弾きます。オーケストラに参加いいですか(“希望者”？)。ありがとうございます。

（日本語がよくできません。Googleトランスレーションを使用しました。ごめんなさい！）

Hello,

My name is Maranda Li, I am the new JET in Setouchi town. Beginning on 7/27, I will be an Assistant Language Teacher at Koniya Senior High School. Pleased to meet you!

I am from America, in University my major was music, and I play cello. I am interested in possibly joining the orchestra. Thank you!

(My Japanese is not very good. I used Google Translate. Sorry!)

We'll see what, if anything, happens.

EDIT: They replied!

Dear Lord I hope it's understandable

Island life, here I come!

On June 22, 2016 I was emailed by the Kagoshima Board of Education with my contract and welcome materials!

On the very bottom of the Notice of Employment, after the signature, was written a small P.S. that contained the name of my school and its address:

I'll be working at Koniya Senior High School, located on the south end of Amami Oshima island, a whopping 220-ish miles (11 hours by ferry or a 1 hour flight) off the cost of the prefecture mainland!