How long has Sai been playing Go?
1000 years

Do Hikaru's parents approve of him playing Go?
It never really said. So I guess the answer is undecided.

Where did Hikaru get his Go board?
Grandfather. To be more precise, his grandfather's attic.

In Touya Akira's school Go club, what nation was the coach from?
Korea. His name was Yun.

Who was the REAL internet mystery player?
Hikaru

I either don't know or forgot the answers to the other questions. :P