It's a coffeeshop ride. 5 miles there, get some tea and scones and 5 miles back. I met the leader, he assured me it was a casual no rider left behind ride. So it doesn't seem terribly scary now that I'm adjusting to the idea

Don't over think this. It's just a 1/2 hour ride to the coffee shop with other people. If the ride leader has assured you that its a casual ride, give him a chance to demonstrate that. If the group leader is any good, he/she will explain the game plan before the ride, and will likely make sure everyone is introduced and go over the details.

On the other hand, if this doesn't happen, introduce yourself to the first person, and the next, and the next. If they start the ride without saying where you are going, or how you are going to get there, or seem to be lacking in other preliminaries (helmets, signals, etc.) ASK. The other riders may assume that you know what they know - which may be everything - or nothing.

If they don't do this, then ask yourself if you really want to ride with them.