Perfectly put. Next thing: You don't start at the front. You start at the rear. The rear wings, "side walls" in BMW speech, are the beginning. Why? Of all side panels the rear wings are the only ones that are welded. Everything else is bolted and can thus be adjusted in the process. Then come the rear doors, after that the front ones. Both pairs of doors have two mount points each and an unlimited amount of possibilities in all three dimensions. The man at the shop swore a lot. Often he called me over to tell me how much easier it is with the Coupés and to get him some trim. Your car is a 2800 Series 1, as far as I remember, it should have a very long trim piece sitting atop the sill. Its outer edge defines the clearance between the doors' bottom edges and the sill. On Series 2 & 3 cars beltline trim alignment is most important because that is what everyone will notice first later. The Series 1 have only a beltline edge but that also should serve as reference.
Then come the front wings and the bonnet. Maybe you'll have to fine adjust the doors again. After that the wings' positions will come naturally. Says the man at the shop. Anyway, they should fit the ears of the front mask quite nicely, at least within tolerance. Look for even gaps between wings and bonnet. Fortunately, bonnet and bootlid as well are adjustable in more ways than you wish to have.
One last thing: Before you paint and mount the front wings look at their lower rear parts. They should follow the straight line of the sills. Old wings do, later ones have the tendency to slightly bend outwards, beginning at the very rear towards the wheelarches. Nothing dramatic but often it makes fitting the heavy, and unflexible, mouldings on the outside of the sills more difficult.