Hi...I live in Champaign. Enjoy the festival...I think you will have fun. There are a number of threads about Champaign area restaurants if you do a search. Downtown Champaign is a pretty concentrated area but has many choices, including a French creperie(Carmons), sushi (Sush Kame) (though a far cry from what you can get in NY), very good Chinese (Peking Garden), a Nuevo Latino place (Escobar's), several places with excellent bar food (Cowboy Monkey, Esquire), an nicer pub place (Farren's) and several sandwich/coffee places (Pekara Bistro and Aroma Cafe). Additionally there is a fabulous English-style pub called The Blind Pig, and a sandwich/late-night dessert place in opening up this Tuesday (the 22nd) as well. Bacaro is very fine, upscale Italian, and Radio Maria is a sort of Caribbean/Latin fusion place, they have an affiliated tapas bar that serves food until 2 am. All of these are walking distance. I think you'll find that there are many people who come each year who will show you the way.
Here too is a link with current comments( disregard the fact that whomever started the thread misspelled 'restaurant'!)
My faves are Bacaro, Farren's, Escobars, and the Blind Pig for a beer. Almost forgot there is Jupiter's for excellent thin crust pizza!
Can't help much between Indy and airport, there are really no sizeable cities in between. Some people like the Beef House near Covington, IN just east of the IL border, but I find it overpriced for what you get.
Hope this helps, you will eat quite well!