I've just received 6 bare-rooted scarlet willows (purchased online). Each
willow comprises 2 stems and is about 5 foot long (bigger than I had
expected!)

To get the best winter colour for next year, I know, I need to prune them
hard. But how hard and when? By a third? More? Now? April?

....and can I use the bits I cut off to generate new plants?

Thanks

John