Internal scan is only if your service provider... And you sure and the hell do not need to make the web gui of pfsense available on the networks that are involved in the PCI..
For example - we are service provider, we host stuff that is PCI for customers... We don't need to scan the management vlan, only need to scan the networks that are directly involved in the processing of the payments..
We are not scanning every single network in the company... You only need to scan the network related to your pci environment.. If your switches and or routers and firewall interfaces are available on your pci networks - your doing it wrong!