If I wanted to freeze this recipe for thanksgiving, would I bake it first and then freeze it, or freeze it prior to baking? Thank you!

I've done it both ways and vastly prefer freezing unbaked mac and cheese.

I've done it both ways and had good results.
However, Cooks Illustrated Magazine (ATK) recommends in its 2004 recipe for classic mac & cheese that the best way to freeze it includes:
1) Cook pasta (& optional veg, in their recipe but not Martha Stewart one).
2) Shred any extra cheese you are adding.
3) Mix sauce & all.
4) Freeze w/out further cooking.
5) Defrost or MW straight from freezer.