One thing the article does not mention: Service extenders are currently for AT&T only. Verizon is on its way (I get 3-5 bars right now in most places in Bancroft anyway), but the other carriers currently do not have a timeline for installation.
Routers are in wardrooms. Most companies will restrict access to upperclassmen only (I haven't heard of a company that allows plebes access, but I don't want to generalize).
Wardroom WiFi is not on the USNA network. Academy network restrictions are not in place. The network is still monitored for illegal activities, but by the ISP. It's like any cable internet you would have at home.
Any device can access the WiFi normally. Routers are managed by company MISLOs (that one geeky dude in the company, likely a EE or CS major).