You can buy a router that has the ability to run as a NAS and let you access usb drives. The router will run fine with nothing connected to the wan port. The only problem I see is how to get the router configured. Most require a pc to set them up initially. Maybe they make one you can configure with a phone. Most do not allow configuration from wifi and if you do you always risk locking yourself out of the router when you make changes to the wifi settings.