Day launching is generally a problem in the Chicago area - getting access and a parking spot are issues. Wilmette does have a big catamaran beach. The next 'burb south, Evanston, also has a launch and sailing beach at Dempster Street. Both, however, are restrictive about what they allow. You might be able to get a launch pass but you won't be able to leave the boat on the beach overnight, and you may have to be very creative about where you leave your trailer, which may not be real close by. From Evanston/Wilmette you'll be 10+ miles from downtown, where the race is. Don't plan to sail inside the breakwater at Navy Pier. I did that once even without a big event going on and will never do it again (tight quarters and BIG boats). I don't think it will be allowed for small boats at the AC event, and it's far from the north shore.
There also used to be a launch on the south side at 63rd street. I know little about it, other than it was run by the park district. There was another at Montrose Harbor on the near north side, but they have changed their minds on beach cats a few times over the years. There will be no camping at any of these places. If you're on the north shore, riding the train or the el is an easy shot downtown, maybe about 30 minutes or so at most. Then you can enjoy all the city has to offer and not have to drive.
Water will be cold. That's about the start of my sailing season and as an old fart I wear a dry suit until the water gets to the upper 50's at least which can be late June. Here's a plot from the South LM buoy from last year:
https://www.wunderground.com/MAR/buoy/2015/6/10/45007.html?graphtype=1&MR=1. There will generally be wind in June, but it can be easy or hard. They're right about the waves being steep, especially if the wind is from the north. The "official" temp at O'Hare may be 80 but on the water it will be about 60 - cooler by the lake.
But let me tell you, when it's good, it's great. There is no prettier skyline from the water, I haven't found a more interesting place to sail, and it's wide open - very few jet skis or motor traffic usually.