I have an HP 4500c flatbed scanner bought in 2004 and at the time I remember that I had problems making it to work and later I found out that the issues was due having 2 usb cables between the usb in the PC and the usb in the scanner ie I was using an extension now I am worried that the scanner would not work well again because I am changing home and now it must be placed 3 to 3,5 meters from the PC.
Would this be corrected with a single long usb cable or a usb hub?
The USB 2.0 specification for maximum cable length without a repeater is 5m. I suggest you use a cable less than 5m. Just make sure you don't use a single 5m USB cable. Use a single 3m USB cable instead. Your printer have its own power source, so you don't need a powered USB port.