While Ubers and Lyfts are readily available in and around Park City, you may prefer to rent your own car for the weekend, which you can do at the airport. If your accommodations are outside of downtown Park City, or if you would like to explore other parts of the mountain (i.e. the Canyons), having a rental may be a nice option! Cars are easy to rent right outside of the arrivals hall at the Salt Lake City airport, which is about 35 minutes from Park City. Transportation will be provided to and from the ceremony on Saturday, and the rest of the weekend's events are in town.
In early September, Park City can be a little chilly (read: light jacket) in the morning, and warms up considerably in the afternoon (around 2 pm - shorts and tee shirt). Evening temps can drop again (think 60s).
Think: cowboy boots and dark jeans, bolo ties, turquoise jewelry, lace, fringe, Beth Dutton at a party.... (But really, anything goes. Be yourself.)
The ranch is on a field, so your best bet are flats or a block heel!