Is Arbitrage Legal?

[Ben4856]

I have a friend in Korea who whats to send me money from Korea to USA and in return I will buy bitcoin and send to him.

Can someone who knows more about this inform me/us any precautions we will need to take?
Is this at all illegal?
Will i get audited by IRS? 50,000 is a lot of money flowing through my bank/
Will he get audited?
Can the money get frozen in wire transfer?

Thanks, I appreciate all the info.