i dont know for sure, but i think some put them in the pass rear. i might put it in the driver side rear, as the pass side loads up on launch anyhow (dips) - plus i think it would be a little less wiring to run.
Definitely a smaller gauge 1 or 0 because of the longer run. Current travels along the outer shell of a strand of wire where the resistance is smallest. Smaller gauge equals more strands equals smaller resistance equals less power wasted heating the wire.