Some of the more technical stuff I'll leave to others more qualified to answer but for a full cat 3 approach the runway has to be safeguarded, i.e. all aircraft at the cat 3 holding points but if they are doing it for training then the aircraft have to told that the runway is not safeguarded.
what distinguishes a cat 3 approach. lots of things including both approach lighting and also lights on the ground, qualification of the pilot and aircraft etc. Also cat 3 ils has much tighter tolerances than cat 1 or 2.