Congratulations, and do go into it with your eyes as fully open as possible. You have already decided to do this, now you just need to look at and prepare for the issues as best you can in advance, knowing you can never be fully prepared.
My best advice (and speaking from experience, though not a Wiccan/Catholic mix) is to make decisions based on an agreement between the two of you about what will be best for your family. That way, if the situation comes up that you want sex and she says no, it’s the wrong point in my cycle, it will be less frustrating to know that it’s based on mutual decision you both made than just the fault of her religion’s views on family planning. If you agree together that you want both a crucifix and an altar in the bedroom or decide to open gifts on Solstice rather than Christmas, it is less likely to become a sore point between you and an irritant each time you see the other one’s symbols. Sometimes it’s the little things that become the biggest problems.
If both of you remain committed to your respective religions, there will be issues, but with lots of patience, communication and looking deep for the reasons, they can be overcome. Sometimes it’s honestly more about culture, family traditions, etc than it is belief. It’s also about knowing that there will almost certainly be issues regarding extended family (my family, for instance, is very fundamentalist Evangelical Christian). Know that these issues will be amplified a hundredfold when you have children.
Google on advice for Jewish/Christian interfaith issues to get an idea of some of the things you may face (and then multiply them as Wicca is not as accepted as part of the mainstream, nor do Wicca and Catholicism have as similar views of Deity).
Also you are quite young (and I presume she is as well). Attitudes, beliefs, expectations, etc can change, especially over the next decade, for both of you, and not just in religion. Realize that issues that may seem very unimportant to you now may become very important later and be prepared that it will take communication and work to get through those changes. We started in our late 20’s and have still changed as people.
From the perspective of twelve years later, a marriage between those of different faiths can work and be wonderful. A lot of talking, a lot of tears, a lot of misunderstandings, a lot of compromise, a lot of forgiveness, a lot of soul-searching and a lot of love, maturing, and commitment were part of the journey, however. We did actually arrive at a similar place after many changes, and are raising our child in that joint religion, which makes thing a bit easier now.
Best of luck in the journey (I’ll get off my soapbox now

, but you
did ask ).