Welcome to our forum.
Your commitment ceremony should be uniquely you, words, gestures, private or public, etc. ... I would assume if you do a word search for "commitment ceremony" you will find some ideas from things other people have done. You can even try that on Google if Polyamory.com doesn't yield a lot, but we have so many threads and members, I'm sure you can find some resources.
Here's one good thread on the subject:
Poly Union/marriage Ceremonies
Glad to have you aboard, hope we can be of help and get to know you better.