The average temperature for September Las Vegas day is around 90*F during the day and around 70*F in the evenings. We suggest you pack sunblock, sunglasses and a light jacket!
We have used the services of Enterprise and have found them to be fairly priced and very helpful! https://www.enterprise.com/en/car-rental/locations/us/nv/las-vegas.html
Unless otherwise directly told, please do not bring uninvited guests. Though, if you are traveling with someone they are more than welcome to join us after the reception down on the strip for the after-party!