There is no 5v in the Wireless controller, it runs off 2 x AA batteries that are 1.5v each and the PnC batteries are 1.2v each, so 1.5v x 2 or 1.2v x 2 is??
0v is ground and you can either attach it to the same spot the GND battery terminal or any of the other ground spots that are around the board. You should have a MultiMeter, plus know how to use it, if you're doing this kind of mod.
In order to do the rapid fire mod on the Wireless you need to use a different IC (provided you're using the 555 Timer chip for it), you need one that will work with the lower voltage.
The spots for the L and R Triggers are the center solder point in the row or three, same as the S-controller L/R spots are.