If you use radius<->router setup, you you need to manage/monitor only radius server, and radius server will take care of all the back-end process. As well as if you go with radius you can go other then openwrt router (I know fully openwrt supported model is more costly and hard to find). you can use those also because you are following industry standards.

And last point if you want to design by your own that is very good, but I'll suggest first go with coova-chilli/nodogsplash (coovac-cilli has more options). Understand its working, then design your own model.