I'm interested in your hardware however, i don't have wifi in the building.
Is it possible to switch off the wifi (in the bios for instance) and to connect a RJ45 to USB adapter ?
It is possible. I have done that before.
One thing to take note, make sure you use the original power adapter and cable. I had random shutdowns while using the USB Ethernet adapter because I wasn't using the original usb power cable. Once I have changed that, all is good.
Yes it works just fine. There are USB 2.0 adapters and USB 3.0 adapters.
One with additional USB ports: http://plugable.com/products/usb3-hub3me Plugable USB 3.0 3-Port Bus Powered Hub with Gigabit Ethernet | Plugable
and one adapter: http://plugable.com/products/usb3-e1000 Plugable USB 3.0 Gigabit Ethernet Adapter | Plugable