Following a guide on how to make something is different than understanding what you’re doing. By all means go for it. I think if you want to enjoy self hosting, skip to that part and come back to creating a router in the future.

Trying to create a router yourself is complicated. I knew nothing about it and installed OpenWRT onto a Netgear router and was unprepared. I ended up effectively taking a YouTube crash course trying to understand so many new networking terms and more. I got it working but any small tweaks could cause issues as I didn’t fully understand what I was doing. I bought a GL.iNet Flint 2 and have been super happy with it. Save yourself a headache, get a good router like that and start having fun running things on a RPi.