What's the best dinner rotation for a 7 day western?
There is no best, they all are great. You're on the ship, you're not cooking or cleaning. Fancy 4 course meal and you can try anything and everything if you want to - without fear of having to pay big bucks for something you don't like. You can't go wrong once you're on the ship.
I know that's not the answer you wanted, but IMHO it's the correct answer.
I've heard people talk about how they would like to have the formal night when they are at Lumiere's. Does it matter?
Once again, nope!!! If you look at Animators Pallette, it's naturally black and white (the walls (with grafitti), chairs, linnens). What's more formal than that!! The only "odd" restaurant for formal night would be Parrot Cay. You know, once you are seated at the table and interacting with your family, tablemates and your wait staff, the theming kinda disappears because you are having a great time with good company (usually) and great food (always).
To me, dinning rotations are not something to stress over. Mostly they are assigned by
DCL and you have little influence upon it (your families make up is the biggest determination as to which rotation you get.)
You need to let some magic come find you. If you "plan it all out" there is very little room for real magic to happen.