I can't help with the shows but here's the weather information:
In Las Vegas, expect daytime temperatures around 23C. However, take some warm clothes because temperatures typically drop to around 4C overnight:
http://uk.weather.com/weather/climatology/USNV 0049?dayofyear=77
(Note that the highest recorded temperature for that week is 34C, so it might get really hot. The record overnight minimum is -4C so it can also get very chilly!)
Las Vegas is surrounded by desert, so rainfall shouldn't be a problem ;-)
Typical daytime temperatures in Orlando should be around 27C, falling back to just 14C overnight. The record high temperature is 33C. At night, the record low is 2C, so (despite the average figure of 14C) it would still be wise to prepared for some cool evenings. Orlando averages 90mm of rain during March, which is about 50% more than the 61mm average for London.
http://uk.weather.com/weather/climatology/USFL 0372?dayofyear=84
Chris