Incorporate oreo bits in cookie recipe
Usually the best way to incorporate any bits into cookie dough is to first mix the dough completely and then mix in the bits - whether it be chocolate chips, nuts, oreo bits etc. This way the bits are not smashed and stay as undisturbed as possible and retain their shape as a whole.

So mix the dry and wet ingredients together to form the dough, then lightly mix in bits by hand (literally use your hands. I find it's the most gentle way) or with the paddle attachment on the lowest setting in a standing mixer.

As for the substituting... Go by volume (Catja's suggestion). I wouldn't sub more than half the chocolate chips with oreo bits, simply because it will make the end result too sweet (because of the oreo filling) and not chocolatey enough. Maybe use dark/bitter chocolate chips as well that aren't as sweet so that you are compensating for the sweetness of the oreo cream filling.