I've been buying these little boxes from AliExpress for years to use as firewalls and routers. My oldest one is almost 9 years old now! OpenBSD installs just fine. Just a BIOS tweak to always boot up after power is restored.
How would one go building a router? I was planning on getting wired networks for a NAS build but most providers seem to ship their own router which probably is a nightmare for privacy, can I just pay for internet and use whatever router I want?