On throw in from out of bounds can thrower step on line. Or does he have to step onto the court side of line to be a violation?

Yes.
On throw in from out of bounds the thrower can step on the line.

The line is out of bounds, so standing on the line is the same as standing outside the line. If you think of it, some courts do not even have a line, but instead the entire out-of-bounds area is a different color than the court.