Best way with FIOS for most is to replace the ActionTec with your own router. If you only have FIOS Internet and no TV service, then you're done. The only thing that you'll lose is their ability to do remote diagnostics. They're used to people doing this by now though so, while they won't officially support your router, they will help up to that point and they're generally helpful if you need support. If you currently have only a coax connection to your ActionTec, then you can have them switch over to the RJ45 Ethernet connection on the ONT. Again, a common request these days and nothing special required in most cases. Obviously, you'll have to put whatever cabling you need in place between the ONT and your router. That gives you your own router up front so that you can use VPN, avoids double NAT issues, cuts out their ability open ports and make other changes on your router, etc.
If you do have TV services, then the easiest/best way is to put one of their routers behind yours on a second subnet and point the gateway to your router. The old red and black ones work fine and can be picked up cheap. That provides the physical coax MoCA bridge for the set top boxes. They don't need much for TV. All that they need for the guide, on-demand, and most other services is an out-going Internet connection. What you will lose are in-coming services like remote DVR programming, using their app to change channels, etc. Technically, you could open up all of the ports required for that to work but since they use a large range of dynamically assigned ports, that kind of kills the whole purpose of setting up your in-coming VPN.
They're also now starting to roll out Ethernet-based set-top boxes which gets rid of the coax entirely so you don't even need the second coax-based router. The limitation on in-coming services probably still applies in that case without opening up a ton of ports.