Length of ethernet cable maximum is around 100m - plenty for the average house
Problem with USB as a whole is it relies on your computer's other resources to handle stuff. Thus network connectivity can be poor, especially if the PC is older and relatively low powered hardware.
If you really do want to use wireless, and since you've indicated you are happy to open the case to fit a USB2.0 card (if you can find one) why not just fit a wireless PCI adaptor card and get rid of the whole USB issue?