It will come in a plane Jane hard case. You can get the toolbox and roll up bag from LT. Recommend at least the roll up bag, it's more handy than I thought they would be.
You'll get some SWAG, never know what's going to show up. Imagine you'll have your rifle before Easter.
You need to buy optics, now so your not kicking yourself when the rifle shows up. Scope mount, BUIS if you want, bipod if you want, light if you want, extra magazines of whatever flavor, and get a form 4 going for your can.
I personally wouldn't order an 18", no real advantage over a 16". I'd have a 14.5" but I've got lots of other stuff with 16" and don't want to deal with another set of tables.
ETA: Also gonna need lots and lots of ammo.