You clear US immigration and customs in Toronto so you'll probably want to be there before 5am. Usually there is not a huge line that early, but depending on the day (Mondays get bad due to business travelers) you'll want to plan to reach at least 90 minutes before your flight.

Good news is that you won't have to clear security again in Chicago.

No food on that flight unless you're in business (and even that is unlikely). Your reservation will tell you it's snacks for purchase or beverage service. Recommend hitting Tim Hortons if you're hungry.