hm, this is more an architectural question than a technical. if you go for one firewall with all 5 networks and alias interfaces and nat-ing, you get it all in one place, but are also creating a single-point-of-failure (that can also fail upon mis-configuration)
on the other hand, visualization with vmware or similar has become quite stable, why not running 5 pfsense installations in parallel? just hook all WAN-if's into the fiber, and then lan-patch-up your customer with or without vlan's, that depends on how the cabling can be done on-site. bandwidth-mgmt becomes then a bit tricky, but getting-started is much more easy, especially if you're new to these technologies. when you're settled you still can change the architecture later on and implement what you learned.
going gold is platinum!