It could never be 10. Ever. It stops being a set piece the moment it cannot have been rehearsed on the training ground. You can rehearse up to 3 passes/touches in a set piece, beyond that, it is unpredictable therefore open play.
3 for me. 2 is obvious, a simply free kick to a player stood 2 yards away, a trap set up, then a shot from a 3rd player is a typical 2 touch set piece routine. Expand this and before the other team can really impact on the rehearsed set piece, a 3 touch is possible within the set piece routine...