There was an article that compared linux based DIY routers with off the shelf home routers and the numbers were pretty conclusive. A basic x86 processor from Intel or AMD is much more powerful than most of the low cost MIPs processors shipped in consumer routers. Why is something more powerful needed? Because the low cost MIPs processors cannot more than a few tens of megabits per second. Here is the article
https://arstechnica.com/gadgets/2016/01/numbers-dont-lie-its-time-to-build-your-own-router/ .
The ISP in my area installs an ONT on the side of your home, it is basically a powered fiber optic to ethernet transceiver and a couple of things, and your home router can be plugged directly into this optical transceiver via CAT6.
You can run the basic services necessary on the DIY router to run your home network, for very basic home network just DHCP & DNS server, and that can be accomplished using the service dnsmasq. If you need wifi you can plug a port from your DIY router into a LAN port of the wifi router (first disable the DHCP service on the wifi router) and use it as a wifi bridge to your DIY router.
This architecture has some other benefits, the main benefit being flexibility. Since the DIY router is running your favorite linux distro you can host other services. An key additional service I have tossed on the DIY router is VPN to provide connectivity back to my home network to provide better privacy and security when using public/untrusted wifi networks using Wireguard (could also use Openvpn or IPSec). Though I agree there are some security implications and running these sevices on an internet connected device is not suitable for a corporate environment, but for your home usage can even attach some storage and the DIY router can also act as a CIFS/NFS server or can run services like OwnCloud/NextCloud.
I've used three APU2* devices from
http://pcengines.ch for different projects and they have worked well. They are low power, I believe they run at 12 watts max, have 4 core AMD processors (supposed to be powerful enough to NAT at 1Gb/sec), 4GB ram, a couple of gigabit ports, PCMCIA, USB, and possibly eSATA. There is no fan or moving parts, I have dropped one or two APU2s on hard surfaces and they have not shown any failure (just a dead AC/DC adapter after a severe electrical storm), they are pretty much rock solid.
Regards,
-Jamie