Dark brown sugar is completely fine. It’ll give you a slightly more molasses-forward flavor, which works really well with the graham base.

Salted butter is also fine if that’s what you usually use. Just pull back a little on the added salt so it doesn’t go too far.

Kosher salt is coarser than table salt. I use Diamond Crystal, which is less salty by volume, so if you’re using table salt, just use a little less.

And yes, press the plastic wrap directly onto the surface of the curd so it doesn’t form a skin while it chills.