I use two devices to handle usual definition of the router:
1. Mini PC[1] running as a router (pfSense);
2. eero to handle the wifi.
Why? I've tried many times to use dd-wrt, openwrt and tomato firmwares on my routers, but every time I failed miserably: it's either something stops working, or I need to schedule routers reboots and so. So I gave up. Since that time, mini pc [1] is the third system which routes my traffic, acts as VPN gateway, proxy server and so on on my home network and I've never been happier. With eero I've got even better coverage comparing to the previous Airport Express.
I found https://www.amazon.com/Qotom-Q190G4-Celeron-Processor-Barebo... a fantastic device for the price. There's a non-Atom Celeron, a Broadwell chip and four Intel LAN ports in a <$150 package without moving parts. My home is small so this also handles the wifi for me.
It has two mini PCIe slots, one for mSATA, one for wifi. It has the usual antenna holes as well. You need an mPCIe card (Intel 7260HMW is popular) and two U.FL to RP-SMA connectors and be done. But yes, you could use USB as well. They sell kits as well but they use inferior cards IMO.
Thanks! I have an ASRock Beebox which has mSATA WiFi card installed by default, but I've never trusted the signal due to its lack of external antennas. I was wondering how well it performs in your setup :)
pfSense is really a good choice, I'm successfully using it for two years without any major problems on a dual-wan setup and some 50 clients.
How much coverage and clients does a single Eero manage - by the reviews I read, I think it shines only when multiple ones are used, but that makes them a pricey solution.
I use a mini PC as router too, running Ubuntu though. It works really well for me. I chose linux instead of pfSense because it is a lot more flexible, and I was already quite proficient in managing linux systems.
[1]: https://www.aliexpress.com/item/Latest-windows-8-mini-pc-min...