You only use fibre to build a high-speed, high-capacity backbone for your network: i.e. connecting up routers, switches, and other networking equipment. Everything else then plugs into your backbone via ethernet or WiFi.
You could also run your backbone on Ethernet, but in the long run you'll be constrained to the limits of copper and the Ethernet standard. The constraints on fibre are way less - only the hardware (routers, switches, etc) needs to be replaced or upgraded to increase speeds and capacity on the backbone network. Your only limit is the speed of light. Having a fibre backbone also helps a bit with lightning protection - especially for outdoor building to building connections.
Another reason for not running fibre literally everywhere, is that 99% of consumer devices have ethernet ports and not fibre ports. If you want to do VoIP, PoE is definitely the way to go. Make sure all your switches have PoE ports, and are managed switches. You'll need to play around with QoS rules, VLANs and spanning trees to ensure that your voice traffic takes priority over other data.
VoIP definitely IS the way to go. You'd be silly to choose an analogue/digital system instead of IP. And even if you don't plan to go with VoIP, get PoE switches anyway. Build the flexilbity into your network from the start. PoE switches are great for rolling out wireless networks - all your wireless access points can be PoE enabled, reducing the amount of cabling required.
Another advantage of PoE, is that you only need to provide electricity backup / surge protection / etc at a single point, at the PoE switch. Makes things a lot simpler and easier to maintain.
