Thanks @yknivag for the thoughts. I can’t remember the name of the missing package, it’s one that lets the setup script create a GUI in the Linux shell.
Just a note, I ran the www.pivpn.io setup script (with minor modification to avoid it telling me I had an unsupported OS) and I’ve had no issues with the server starting up - it comes up just fine on every reboot. The entry it created in iptables is persistent across reboots as well (as far as I can tell).
Assuming my setup is now working (I’m posting this while connected to the VPN), the whole process was remarkably easy - the setup script pretty much took care of everything (and I suspect my routing issue was my own fault for entering something wrong during the script).