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.
You could do that, I'm not sure what the performance will be but there are adapters that you can buy and try, I have not done that myself, but Choong has confirmed that he has done it as he mentions above.
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