Shusuke probably couldn't be friends with anyone outside of his Clan. Becuase he is the king. And the king has nothing but enemies >_> lol XD
No but seriously I have no idea. 

Anyway...
He probably wouldn't leave Japan. He is pretty much always on vacation. He does like anything he wants as it is XD
Aside from current problems he has fun. 

Also I'm pretty sure if he left the area that the Dresden slate effects he would lose his powers.