The questions 1,3,4,5,13,15 are already answered.Let me answer some of the remaining questions.
2)Let us assume the lines to be X,Y axes for convenience.Then,P(x0,y0) belongs to the locus iff Ix0I+Iy0I=1.Thus the locus is a square formed by the lines IxI+IyI=1 with centre as origin.
MAKING A MISTAKE IS HUMAN BUT REPEATING IT IS IDIOTIC.