Chicago hits different in shoulder season. Head out in late April or October to skip the brutal winter wind and dodge the steep summer hotel rates. You get crisp walking weather, smaller crowds for the architecture tours, and easier table reservations.
A solid weekend trip runs about $1200 all-in for flights, a good central hotel, tours, and food. You do not need to drop all that cash at once if you plan it right.
Remember that a 0% intro APR is a strict deadline, not free money. If you still carry a balance after the 15 months wrap up, standard interest rates kick in on whatever amount is left.