Congratulations on your upcoming wedding. Coincidentally, I got married in Milwaukee and now live in the Chicago area. However, we make frequent trips to Milwaukee to visit my in-laws.
I'm glad to hear you are thinking about your vendors. There are a couple things to keep in mind when planning to tip the vendors. You may be paying the venue 18% service charge but the serving staff will not see a single penny. To make matters worse, they can't even so much as hint to you that is the case.
Now let's talk about all your other vendors. They will either be an employee of the company or they will own it. If they are the employee, you should make sure they receive a tip. For they are getting paid a set amount with the owner taking the rest of your fees to cover costs and provide a profit. When the owner is actually providing the service, they figure in their pay/profit into the price they are charging you. The best tip you can give an independent contractor is to refer all your friends to them. But if you really like their service, there is nothing wrong with giving them a tip too. As I tell folks, "A tip is not required, but I do appreciate it" Please let me know if you have any additional questions I might be able to answer for you.
Howard Kier, Certified Professional Wedding Photographer
As previously mentioned, tips are optional but appreciated by most people. At most venues, if the service charge is 18%, 15% is split between the servers and 3% goes to the banquet captain. If you are having an outside caterer come to a venue, check their invoice to find out if they added a service charge. That said, should anything happen that requires one or two servers to go above and beyond what they would normally do, such as cleaning up a huge mess, then give them a personal tip.
Limo drivers who do not own the limo typically receive a tip. If the florist or cake baker charged a delivery fee, then no tip is necessary. If they included the delivery in their service, then a tip toward gas is appreciated. Photographers are not usually tipped. Some DJs require a tip; others don't, so do what you feel is appropriate.
Even if you don't give a tip, do send a thank you note to everyone working at the wedding. So often vendors hear the negatives but they don't always hear the positives. A handwritten and mailed thank you note is really appreciated.