Shades of blue, in dressy causal clothes
The warmest weather of the year in Banff is definitely in August. The temperature is around 70 degrees. However, it gets cold at night so pants and a jacket are suggested!
Yes. It is the busiest time of year. You’ll need to arrive at the parking area early, around sunrise, to score a parking spot at the most popular spots like Lake Louise and Moraine Lake.
Comfortable walking shoes, an outfit for the wedding, and layers! Here's a blog with a more detailed list: https://thebanffblog.com/banff-packing-list/