This is a great question! We follow up with Catholics the same way we follow up with everyone else.
What I have found in my experience with Catholics who come to know Jesus is that they know a lot about God, but just don't know Him. (I know I'm generalizing and that this can be said of many people, so please forgive me for painting with a broad brush.)
But one thing that I've seen in Catholics when they invite Christ into their lives is a hunger for God's Word. They want to learn God's Word. That's why any follow up plan for new believer MUST include a means to educate them in the Bible.
So here's what I suggest: Develop a plan for following up with new believers that includes a new believer's class as part of the process. This will increase you retention of new believers and will kick start their discipleship.