You do not need the Verizon router as the primary router, but the default install is MOCA coax to the WAN port. Have the tech turn on the Ethernet port at the ONT, and install the Verizon router with the Ethernet wan port to make sure it works. From what I have heard most techs want to use coax, and do not want to use ethernet. Perhaps they don't all have RJ-45 crimpers or know the pin outs. If you have a good ethernet cable pre run from where the ONT will be located, that will help you fight the battle. If any trouble shooting is required, they will want to have their router as primary. But after the tech leaves, you can switch your router as primary.
PIX --> Ethernet --> FIOS Router So that we get the internal 10.net address on the 3 ports (Ethernet Ports 2,3,4) and wireless.
ONT Ethernet - WAN - IPCOP Linux based router LAN - 16 port switch - Verizon router's LAN- Wireless and MOCA.
I use no WAN port on the Verizon router. My IPCOP Linux router issues all IP addresses, firewalls, filters, and logs everything. Even runs transparent proxy for the Web, so all web traffic is logged. All on a cheap AMD Single core chip, 512meg ram, 80gig HD.
PIX should work fine. But my public IP used to be in a class A subnet 74 range, but has since been taken to a class B. It was a little better before. If you have a business class FIOS and pay for fixed IP, your service should be better. TOS restricts servers on a residential service, and blocks some in comming ports. All mail needs to forward through Verizon's mail server. I am not sure what DSL has been doing, but these SPAM wars have been a pain.