If I want to get a full set, how many items would it be? Is it 16, or 17(with hair color) or 18 (with hair)

probably 17? or no?

17. Can be with or without hair colour.

It's still considered a full set without the hair.
If you want to get the achievement, it's with the hair now.

Yep, I confirm that. 17 items is needed for a full set. It's unfair, but still. (It used to be 16 items plus hair color is VERY expensive, well, some of it)