We recommend walking to the venue, it's only a few blocks away from the hotel (about a 5 min walk).
Street parking is free all day Saturday and Sunday. You can also pay to park at a nearby City of Milwaukee public surface lot, the Library Lot, or the Wells Fargo lot.
Cocktail attire. The ceremony and reception will be inside, but cocktail hour will be outside in the courtyard. It looks like it might be warmer side (high of 88 degrees), so keep that in mind!
Casual cocktail attire with an emphasis on the casual side. Really, whatever you feel most comfortable in!