Probably wishful thinking, but is "Arra a belga fiú sétál amerről a kinai lányok jönnek." correct?
It is correct, yes, but maybe a bit unusual. It would be more normal like this: "A belga fiú sétál arra, amerről ... "
I think in general the form of "az" (arra etc.) should be placed either directly before the verb or the comma.