I'm starting to paint these figures and it seems they all have sashes over the left shoulder.  Am I right or would only officers have sashes (but over the right shoulder)  ?

My reading of the ECW would seem to suggest that any cavalryman at that time who could afford it would wear a sash to show his allegiance (to either a cause or to his commanding officer), eg. I read that Haselrigge's cuirassiers often sported his colour by wearing green sashes. TBH most are shown with the sash around the waist, Although a little dated now, Haythornthwaite's The English Civil War - An Illustrated Military History, Blandford Press 1983, has colour plates of Cromwell with his sash about his waist, acuirassiers trooper with no sash, a cuirassiers trooper with sash over the left shoulder, a trooper of the King's Lifeguard with sash over his right shoulder, and Col. Alexander Popham in full cuirassier armour with no sash at all.

Thank you for this helpful information.  I didn't realize sashes were all the rage:)

Sashes, or more properly 'Scarves' were an issue item for Horse and Cuirassier units.  With both sides using very similar equipment it was a simple means of identification in the heat of battle.  At Marston Moor, Fairfax was able to ride away from the disasterous ruin of his wing of Horse and make his way back to friendly troops by the simple expedient of taking his scarf off!