Hi Marc,
The combination of 5M active and 3M regular will work fine. The "active" part of the extension is really just a one port hub that helps retime the data and basically clean it up so that it can go another 5 meters. So as long as you have one every 5 meters or so you should be fine, factors might include the quality and age of the cable and quality of the port inside the computer.
I don't know of any special break-away usb cables, I was just referring to the idea of using a short cable loosely secured to the tripod so that if I, or someone else, trips on the cord it would unplug instead of pulling over the camera or harming the usb port on the camera. We use the plastic clips that come on Bogen tripods and booms.
Dave