My nephew came to Japan 3 years ago, he was 8 years old at that time. Unlike your son, he has never heard a single Japanese word his entire life before coming to Japan.
Like you, International School was out of the question. He was sent to a public school immediately. His step-dad is Japanese and was the one who tutored him. The school is very accomodating too. I guess having foreign kids was not new to them. He was give some make up lesson to improve his Japanese.
Of course, having only Japanese spoken inside the house really helps a lot. In a year he was already fluent and his Kanji was doing OK. I guess it was all thanks to his step-dad and his new grandma who really put some effort and lots of patience to teaching him.
His mother , my cousing is useless in that department as she can't barely hold a decent conversation too.
Kids adapt really quick , and of course your husbands help is really important this time.
I think the most expensive they bought for him was his bag which cost around 30,000 or 50,000 yen, but his dad said that it will last till he graduate grade school.
Every month, the school send food menu to each family so you will know what your kids were eating in school.
Also for you, if you want to continue studying Japanese, check out your local community center, city hall for volunteer classes and activities.
Good Luck.
