4. Hirai's position within Ueshiba's organization is actually rather odd. He was the general manager of the dojo/organization, yet he maintains that he was separate, that he'd created his own martial art from his variety of studies - that, nonetheless, really looks a lot like aikido. Parallel evolution? Why, in fact, is it called Korindo Aikido, which is sort of like Kendo Iaido or Judo Karatedo. Yet I've never seen anything, even obliquely, from the Aikikai that criticized or questioned Korindo.
5. Anyway, the only way to get an answer to this is contacting someone who is plugged in to the prewar history of the Butokukai. I will make an attempt and get back.
As a student of Korindo aikido, I do have a couple of comments on 4, from items which were told to me (not real historical proof):
a. Hirai was a teacher starting his own path already before he moved to Tokyo and took the role of "general manager of the dojo/organization". Further, Hirai moved from this position to the position in the Butokukai. As far as my teacher asked in the "new Butokukai", they claim back then there were no "representatives", definitly not for Ueshiba (I would guess back then he was not considered too important himself).
b. Maybe it's just me, and my very limited experience, or the passing of time. But in the one lesson I did take with Takanaouchi ryu, I found that "korindo aikido" looked very much like it, as much as to Ueshiba Aikido. Then again, I see the same similarity viewing other styles of Japanese Ju-Jutsu (either that or similarity to Judo or some combination).
And as Hirai explained in the past the name "Aikido" itself is not even his own suggestion.