I have a partial solution. It turns out you need a Verizon data plan with a fixed / public IP to be able to see the rCell from outside. (Bring money!)
So now I have initiated contact from the outside to the rCell. I have a known-working communications link. That’s good!
Work on the OpenVPN configuration continues.
Now I have additional questions:
The manual seems to suggest that if I want to expose other devices on the rCell end of my VPN link I need to configure a VPN server (with a push route) AND a VPN client on the rCell. Surely this is not correct! Can anyone confirm or deny this?