hi,
I read your description, and it's completely possible.
Which router model are you going to use?
Openwrt is fully open source, and customizing openwrt is easy.
I use ubuntu to compile openwrt and I mainly developed TL-1043ND v2, Asus N13Ub1, Netgear routers, Cisco Routers, mikrotik routers, etc.
Changing Admin username, password, ssid, wifi password, etc are just changing settings, so it will be no problem.
I will provide you the perfect result that you want.
Regards,