Nice! I wrote about my experience as well in case it's useful, https://skogsbrus.xyz/blog/2022/06/12/router
It's a bit long, but the title sections should let you skip to the interesting bits.
Here's the latest code as well: https://github.com/skogsbrus/os
Sources: https://discourse.nixos.org/t/do-you-use-nixos-on-your-route...