I think the longer u hold it the more chanc of winning but I do try to time it to release on contact .
Re goal kicks I'd try passing it out, or a really short lob pass to someone open. I think headers from ur own gk are very unlikely to be won as their teams coming on to the ball, If u do go long try aiming your header sideways or back towards ur defence if u want to keep possession whilst someone challenges u in the air.
I agree with above that scoop turn ( especially the 5 star version) is hard to defend. Next skill move to learn doesn't need much skill. It's called changing lanes or changing tracks at least it used to be, basically just drags ball to the side. Good for when your running head on at defences and u can see one about to slide you, also good for changing the angles of through balls. Basic but effective
I'm looking at lists of the skill moves and see the 4* standing scoop turn, but dont see the 5* one, is it called something else?