I just bought a new (old) house and I have a couple of questions. Our
underqualified although state licensed (Wisconsin) inspector missed
some extremely obvious Knob and Tube wiring which turns out to be half
the house so I'm rewiring most of the house. The first question is:

Do I have to remove all of the dead knob and tube wiring?

The second question is:

I'm running armoured cable to the attic to replace the Knob and Tube
and the cable is running in an open cavity between two bedrooms. Do I
have to open the wall and secure this every four feet?

Thanks,
Gavin