5-10 is a good starting point. Depending on where you are in Rantoul will depend on your predator pressure. I spent about six months there and my DW grew up there. Checkout the articles, especially those about coops and runs or mobile coops. Get everything ready before you get your birds. If you're within the city, likely you will not be allowed to have a roo.
Now for the hard part... FEED! The choices are endless the supply is not. Do you want organic or do you care? Do you want non-gmo or do you care? Do you want soy free or do you care? all of these choices will drive you nuts--but learn early so you can make informed decisions. Organic is by definition non-gmo--but not soy free. Personally, using the right soy in you feed is good--but that is a whole other conversation.
Do you want your birds to have access to fresh grass or be cooped up in a run that resembles a moonscape? If you choose fresh grass, can you have electric fencing? Check your city ordinances. I put my babies (3 week old) in an 8X8 shelter and keep them there for 5 weeks, then release them to a house on pasture, with electric fencing. While in the shelter, I move it every three days for 30-40 birds. Good chickens will eat a LOT of grass. And leave you plenty of fertilizer to re-grow it. And they'll degug your grass as well.
Don't know if this was helpful or not--but feel free to ping me with questions if you like. I don't know all or even a lot of the answers, but do know a lot of smart people.