Going las vegas beginning of september. where do i buy tickets for shows, tour& what do i do when im there.?

what shows can you recommend we want to get the most out of are time there as only there 5 days. should we pre-book tickets? what is an average cost to see cirque de sole? (not sure how that is spelt) where do we book grand canyon tours we really want to go by helicopter but want to see hoover dam also. where is the cheapest to book this and helicopter down the strip or is it cheaper to book once there? so excited about this trip it is for fiancee 30th so want to make it really good. any other tips and suggestions of place to visit things to see would be much appreciated. where to eat places to bet and how to bet! lol were not gamblers but no doubt we will have a flutter.