Bought mine in advance of new car, it comes on an A4 certificate, just give that to the supplying dealer when you place the order, and they’ll use that to register the new car once built, and it will be collected with the new plate.
I bought the plate in my wifes name as it’s her lease to avoid any issues, the dealer will sort out the registration of the car, but you will still own the plate to transfer off in the future.
i should add all previous cars had year plates but this time we added a private plate as you are doing.