This is a great tutorial on setting up AirVPN (can easily be applied to any VPN provider) on pfSense 2.3.x and VLANs. I had always meant to update my guide for this. I had written:
NOTE: FWIW, I think you could accomplish this through VLANs [rather than static IP addresses]
The author goes through the details of setup, including VLANs as well as hosting your own DNS resolver. It’s a great job.