Where is a good meeting place that's easy to find for someone who has never been there before Is? Is the visitor's center right at the park entrance?

Best place is to meet at rock creek across the street . Smaller area that's consolidated . You will find your person.

It's easy to find, but it has two entrances and converges into a Y eventually. Maybe just past that point in the first pullover. There us a visitor's center at the west entrance.

Yes, the visitor's center is probably the best place as there are signs (Brown) from both directions to the visitor's center parking lot entrance.