I would suppose set up will depend on the bike you ride. If you teaching on Keiser bikes, I'd follow their set up protocols, I don't know how different they are from the JohnnyG style of Spinner that Schwinn and Star-Trac make.
As for which to set up first, I set up seat height first, because I gauge it by the top of the pelvic bone, before the person gets on the bike. Seat fore and aft is next, with the person sitting on the bike. I use elbow and knee alignment, with feet on the pedals at 3:00 and 9:00 parallel to the floor, to gauge proper seat position, fore and aft.