Thanks for the input on the rental everyone. I plan on renting through theblacktux.com as a good friend's sister works there and another friend had a positive experience at a recent wedding.
For those of you who have attended more events like this how does it work in America (downtown Chicago, October wedding):
3pm Catholic service, large 20 person wedding party
5pm Cocktail hour
6pm "Formal" reception (Live band, very nice venue)
I understand that black tie is traditionally evening wear - is the expectation to have two outfits for the day? The groom is a cousin of mine, and I can reach out and ask but I need to make sure I don't do it in a way as to say "you don't know how this works"