I realize you have ides of your own, but I have been looking for an app that is a simple wifi manager for connecting stations. I think this would offer you a project with wide appeal and more feedback than, while very kool, a home automation hub. Easier to learn when you have more users to test.
As there are no “APPS” for OpenWrt that I am aware of it’s wide open as far as approach.
For a connection manager, it would be easy to store all the connection data on the phone, including login to the router. It should be about 2 clicks (open and scan, then select) and a key.