Both approaches are equally stable. There are situations where you would choose one over the other but they have nothing to do with stability. Usually, you might choose a rule when you have more than one type of Item in the Group or if there is some state you want to take into account for some of the Items.
Depends on the situation. There are some technologies that become overwhelmed if you bombard them with too many commands all at the same time so a pause is used to keep that from happening. Other times people want to spread out the commands to achieve a certain effect.