I will be cosplaying Tear in a few months, and I have yet to start the costume, but maybe I can help.
For the dress, I have a very simple dress pattern that I'm modifying to look like Tear's uniform. I'm making it longer with the side pieces seperate, and putting a zipper up the front. For the collar, just make it extra wide and line it with some stiff interfacing.
As for the wig, I'm not sure if I'm wearing one yet, because my hair isn't so different from Tear's and I already have to buy wigs for my other 2 cosplays, but maybe this one
in Honey Sweet will work? If I do get a wig for Tear I'll probably use that one.
Hope that helps!