How much of the outer sheath should I strip back before terminating the cable?

The original installation instructions suggest stripping approximately 30mm of outer jacket to give enough working length to dress the four pairs into the IDC. That is a preparation length, not a target for leaving 30mm of loose conductors behind the finished module.

Bring the cable jacket as close to the termination area as the routing allows, keep the pair twists intact until close to their IDC positions, and let the punchdown tool trim the surplus conductor.