After decades after observing what goes on, it seems that the order of Kibudim varies by community.
While most people treat
מסדר קידושין as the top Kibbud, sometimes it belongs to the local Rabbi, irrelevant of who else is in attendance.
Spot number 2 has 3 contenders:
First 2 ברכות and
There's another Kibud (location dependent) that is parallel (or replaces)
קריאת כתובה: The Speech - which also usually belongs to the local Rabbi.
As already mentioned in the comments,
קריאת כתובה is often given as an important Kibud to a VIP one rather no have involved in the Halachic parts of the ceremony.
Other times it is given to just anybody whose sole qualification is that he understands what is written so that he can read it fast and sensibly. (That's how I once got the Kibud, even though I was merely one of many work-colleges in attendance.)
BTW: In some communities all 7 Brachot are given to the same person, typically the Chazzan.
Witnesses are often chosen on technicalities rather than merit, as you don't want them - or their spouses - related [even remotely] to each other or to the bride or groom's families. Even though remotely related witnesses may be Kosher, most מסדר קידושין prefer not to deal with it.
And don't forget Common-Sense. Keep the short brachot for those who will have trouble with the longer ones: A frail grandfather, an non-scholarly uncle or a shy brother, for example.