You want to distinguish if this is
AWARENESS vs LEAD MAGNET
In this case I believe this IN PERSON WORKSHOP at your church would be AWARENESS
This is YOU getting in front of "other people's audience" to increase awareness of what you do.
You want to get AS MANY PEOPLE AS POSSIBLE here.
BUT your goal here is NOT in this case to get leads (people on your list) because that is the job of the LEAD MAGNET (5 day challenge in this case / starter kit on this diagram)
The only reason to get them to register for it in advance is if they don't normally gather at that location and you don't want to bring a bunch of props if no one is going to be there. But asking for emails, phone numbers etc. in general will DECREASE the number of people who show up and we want that number at the top to be as BIG as possible.
(See next step, Six Figure Health Coach Funnel System Visual)
Now sometimes the "talk" is actually a "Video Sales Letter" - webinar that IS a lead magnet. They have to OPT IN with email at least to get the video training ... and then it can be designed to get people on your call. This is a different talk than a workshop although there is certainly overlap with your story and slides etc. In this case you would have a landing page for this lead magnet just like you would with a 5 day challenge.
I recommend keeping it simple.
I would not ask for anything for this workshop in this case, BUT I would promote the heck out of it. Tell everyone. Get everyone to bring a friend. Put it in church bulletin. etc. etc. Bring 10 people yourself to it. More the merrier.
Sometimes if it is not a community you are a part of, sometimes it is helpful to charge so people will show up. But it is way better if they are already meeting there anyways - like a corporate lunch and learn. Or a church event where the community is used to going to events there on occasion.