One of the reasons I like the idea of the Minbari being Earth's 'first contact' is that I could then use the Vulcan/Andorian conflict/cold war as the 'first contact' opportunity for both races, which would help cement Earth as a major player in interstellar politics and whatnot and make for a bit of an interesting transition to both the Vulcans and Andorians being part of the founding of the UFP, since the Enterprise and her crew would be a key player in the cessation of hostilities and animosities between the Vulcans and Andorians.
I did just think of a way to offset the Minbari's technological superiority with where I'd like Earth to be, which is that the Minbari keep most of their technological advances secret.
I hadn't figured out a way to bring the Vorlons into things, but I do like the idea of them taking the place of the Preservers, Progenitors, and the aliens from "The Chase", and also sort of filling the same role - eventually - of the Organians, albeit much more 'behind-the'scenes'. I could also tie them into the reasoning behind the Minbari keeping most of their technological advances secret.