ND,
A workshop is a good idea. I usually just make sure I day paddle first with anyone I invite on a longer trip. People tend to over state their experience level. A half hour watching them paddle tells the story.
Evaluating personalities and trying to figure compatible paddling partners is the wild card. It is not that easy to assess. I have lost one friendship because of paddling, and messed up a few others, that mostly got repaired later after the trips.
My friends are getting older. People are vulnerable on a canoe trip. They are out of their element to some extent. They can have various kinds of melt downs and get overwhelmed. I am no longer interested in bigger groups. I only paddle and row with a few trusted friends and dogs now. My dog and my brother are my two best paddle pals.
PS I have no long list.