Could I also add walnuts to this recipe with the chocolate chips? If so, do I also add it in with the chocolate chips to coat?

I agree with Nancy. Mix them in with the chips or press them on top before freezing.

I would go ahead and add the nuts.
If they are bits or chopped, mix them in.
If beautiful half nuts, I would press one or two into the top of each cookie after shaping and just before you put them in the oven.