Whether he needs it or not, he should get it as a reflection of his ability to control his body more and more easily as he advances through the class. I don't know, it just makes sense to me, that's all.Immediate actions do exist in Core (e.g. casting Feather Fall), if not by that name, but I don't really see any reason that a monk should get that ability. (He also shouldn't need it; most magical protections are duplicated by his class abilities, and those few that aren't, such as Fly, can usually be duplicated by items (which ignore his SR when he's the one using them.) Throw in Soulspell so even a CL 5 Fly can't be easily dispelled, and he should do just fine.
AlrightI'm not quite sure what the question is. If the target succeeds on their save, nothing, if they fail by less than 5 it paralyzes them one round, if they fail by 5-9 it paralyzes them until they make a successful save (the save is a free action, so they could, for instance, cast a silent stilled spell in the same round they try to make a save to break it), and if they fail by 10 or more it paralyzes them until they make a successful save (the save is a full-round action, so they can't cast a silent stilled spell that round.)