As it's been stated before, welcome to the jungle. Missouri is a OC mess because every county, city, and municipality can make their own laws regarding OC. Since MO honors your WI CCW, the state law has the authority. Read the law to see where you can carry concealed. As for OC, where are you going to be? If it's St. Louis city/county, just make it easy on yourself and conceal. Just about any other part of the state is OC legal, but you still need to read the laws regarding those particular county, city, and municipalities. Let us know where you'll be, and we might be able to shorten your research a bit.
Also, MO has what's called the peaceable journey exemption, meaning that anybody over 21 can carry a firearm, open or concealed, anywhere in the vehicle or on their person, even without a CCW. So as long as your in your car, you have nothing to worry about. But, once you step out, know the laws on OC (or just cover it up).