The idea was mentioned in the guide above already but it wasn’t explained how to setup the vm’s in detail.
So far I made the following:
Whonix-Gateway vb Adapters: 1. NAT 2. Whonix
pfSense vb Adapters: 1. Whonix 2. pfSense
Whonix-Workstation vb Adapters: 1. pfSense
also I did some experiments with LAN/WAN-IP settings (e.g 192.168.0.xx/24 in different ways) but none worked for me.