I'm gradually getting there.

What I do not quite like yet is that the line doesn't bend 100% smooth. But more importantly, I just can't seem to get a bigger arrow at the end of the line, without having to go for the "Colossal" line end size.
It seems as if there is a size limit for custom line ends, at least when they don't have the "Scaled" property (only then they automatically adapt to the line thickness).