I did something similar (not a router, but we considered it), and its not that difficult on the hardware side. Our home automation hub was just a Raspberry Pi 3, and had more than enough power.

If I were doing this just for my own home I'd probably get a half decent NAS capable of running Linux and then run home-assistant.io on it rather than building everything from scratch. Home Assistant gives you a decent UI, integration with almost any hardware you can think of, programmable automation, and an API to build against if that isn't enough.