The OP is asking about the dealer placing the order on the Motability system though, which can’t be done in advance!
Was pertinent in a way though as the OP asked for any help/suggestions and the fact that he can get most of the background stuff done online in advance of the visit to the dealer will definitely help. I’ve just done all that, but was unaware until I started looking at my online account and it made the dealer visit a lot smoother.