I have no idea. I'd probably tell them how you envision the day and see if they have any ideas/suggestions. Maybe ask how many weddings they've done before (and if its possible to contact the couple(s) for a reference/view footage of the ceremony being conducted). Oh and I'd ask them what information they'd need from you and if it's possible for you to have a read through a draft of the service they'll be conducting before the big day to make sure you're happy with it.
When my friend died a few years ago, his parents hired a celebrant to conduct the funeral service. Apparently the first draft, whilst factual, just didn't quite sound like the friend we all knew. The celebrant was absolutely lovely and happily re-wrote it until the family were happy and he even contacted us all through the book of face for stories that could be incorpporated. He'd dedicated so much time to writing his service that by the time we all turned up for the funeral he was able to identify and welcome each of us by name and the whole thing just felt so personal. He then opened up the floor to anyone who hadn't already been asked to speak but felt they'd like to say a few words. If a wedding service is anything as personable as that funeral then you're in for a very wonderful, intimate and unique service. We decided not to go for a celebrant though as we both hate being the centre of attention and want the ceremony over and done with as quickly as possible.

Had the meeting with him last night and the gist of it is... anything goes. The only thing that we HAVE to do is the legal stuff. As long as we have two witnesses and recite 14 legal bits of text the rest is however we want it. Any music etc so very relieved.

And Showgirl you are pin point accurate, the whole point of the ceremony is that it's about us. So he took us through the wedding "journey" of how he normally likes to conduct a ceremony and how before hand he will sit down with us a lot learning about how we met, how our relationship evolved and anything that really makes us... well us. He will engage with our guests as well so talk to and with them instead of just at them. Both H2B and I left very excited and I couldn't help but pull a cheesy grin when he said "... and then I would say I am proud to say you are now husband and wife"

Dammit being a year and a bit away!

Oh it's going to be such a magical service - make sure you get someone to film it, you'll want to play it back over and over again! I'm definitely going to book a celebrant to speak at a milestone anniversary down the line...