This is totally your call! You definitely don't have to...Lyfts/Ubers can get you pretty much anywhere, and there's also a convenient train that runs from the airport to Union Station in Denver. See "Getting Here" page for more details. If you want to do any exploring outside "home base" (a hike, a trip to see Red Rocks, etc.), then it's probably more convenient to rent a car. And if you do rent, parking is pretty easy!
There will be transportation provided to and from two pickup spots. See "Transportation" tab at the top of the page to see more information. You can also Uber/Lyft or catch a ride with someone who has a car - there is plenty of parking at the wedding venue!
See "Schedule" page for specifics for each event! In general, plan for days to be quite hot and evenings to be in the high 50s, low 60s.