The Wii U has 4 USB ports, so as long as you aren't charging multiple Pro controllers or leaving Skylander/Infinity portals hooked up you should have more than enough space for the Gamecube controller port, an ethernet cable and a external Hard Drive. I'd recommend finding a way to get the ethernet cable hooked up, as a secondary router will increase the amount of interference in your place (you'll have a secondary access point but double the WiFi going through the place. Could potentially cause lag, depending on where you live.)
If the distance is too far for the router, you can see if you can get the router moved closer (possible with DSL internet, since it uses the phone line) and then wire things up. This is how I got around the issue (I live in an apartment, so interference made the WiFi unreliable for smash), as I moved the router in the same room and then with CAT6 and a switch got my entertainment center all hooked up with ethernet.
If you can't move the router and getting Ethernet hooked up is impossible, then it's on to wireless optimization options; like changing your frequency, checking for QoS options that maybe strangling the little quality you are getting, etc. There are plenty of threads created, some even by me, that will cover some of the options available to help ease your pain.
Hope this helps.
