Do you want a trailer you can sleep in? Ours is a 20 foot trailer. the back 10 feet are kitchen, the front 10 feet are sleeping/storage. I do several events a year where I need to be on site, plus for the competition side it is nice not to have to sleep in the pickup truck.
BUT I really wish the kitchen had more room. Get two people in there and it is tight, get three and I'm getting clostrophobic.
Speak with the local Health inspector, but also with other Illinois vendors. IF Illinios inspectors are anything like Iowa's then you will get ten different answers by speaking with ten different county inspectors. Speaking to other vendors sometimes helps to sort through what the inspectors are trying to tell you.
What we did was to find a used trailer that someone else has already had licensed and inspected, had a buddy who has worked in BBQ for years inspect the trailer before we purchased and then after his approval we bought it. It passed with flying colors.