I just came off another test session. I'm up to four companions, all running on one script - plus ED-E.
Thus far performance continues to be excellent, for the most part. Holes and errors in the game's navmesh are prolific to put it mildly; and these naturally give any followers pause. Considering that ED-E stops whenever the NCCS followers do, I'm inclined to believe it a game-wide engine problem, and not some hole in my work.
Script issues aside; my previous conclusions remain. Parties greater than four simply aren't practical in the game; they make it too difficult to move through tight spaces, and friendly fire is nearly constant when they start shoving to get to the front of a firefight.
Issues with the companions attacking anything that tried to attack me remain. Despite pulling the code that triggered it. It seems to come up whenever an actor or creature attempts to target me. Don't know that there's anything I can do about it, either.
That said, the system is as good as I can make it at present; and any further delays would simply be procrastination on my part... so I won't.
Miss Herculine has turned in a version of her pack that's updated to work with the latest beta master, and my own is about as ready as can be.
I still have to take some screenshots, write a readme, and throw together some sort of companion creation guide. After that will be upload time.