Unfortunately many quest related followers take different "spaces" in their... queue trail... What I mean is: Someone like Brother Verulus will stand farther away from you if you have someone else taking the "two" position. I have no where near as much experience with tag-alongs as Harkin, but from my experience, I can place a few NPCs:
Position #1: Barbus, Thonnir
Position #2: Typical Follower, i.e. Jenassa, Lydia
Position #3: Meeko
Position #4: Brother Verulus
Position #5: Thralls
What this boils down to is, you will have to deal with a very long follower trail. There are a few major drawbacks to having all these positions taken up: The first is that if you do have thralls, they will never be by your side. They will lag behind at such a radical distance that sufficiently takes them entirely out of fights in the open world, or even in larger dungeons. Instead of running up to meet the foe, they'll walk around cautioned, as if they don't know where to go. Yea, they're that far back! Another downside is, cramped spaces become quite unnavigable and inconvenient to go through.
I did run into a rather interesting consequence however. With so many positions taken up, places like the hidden entrance to the Thieves Guild and the Arcanaeum spawn you beyond the stairs. No more pull chain required! And such in the Arcanaeum results in you appearing right next to the librarian. Literally. Unfortunately I found the College to be very upsetting for my 360 with these followers. It would freeze every second transition, no matter what the scenario.
edit: I should also mention, Enmon behaved like a slot #1, though, he wasn't anywhere near as intruding as Barbas or Thonnir. And followers like Cicero I am in the dark about. I know he'll stay up and close; however, I do not know how he adapts with so many others in queue.