No. Denver is located at ~5000 ft of elevation, which usually does not cause elevation sickness. Just make sure to drink plenty of water!
Denver is known for over 300 days of sun a year! However, we do have the occasional storm that passes through (usually quickly). An average late November day is 55 degrees and sunny during the day and 30 degrees at night.
This will be dependent on weather. If it is a nice sunny day, the ceremony and part of the cocktail hour could be outdoors. However, dinner and dancing will take place indoors.
Please check the website as the wedding date gets closer for more information.
Please dress in semi-formal attire.