[quote=@Ariamis]
How many vassals does the leader of ACA have, and how many fiefdoms do the vassals have? I understand sizes may vary for the vassal's domains, but how large are they on average? What's the average number of magical girls and/or normal humans under the flag of a vassal?
[/quote]

Geez, ask me some tough questions why don't you? :p

I'll say five direct subordinates, with the territory divided up based on Witch concentrations, but still covering ~5/6ths of the city. The last part is for our Glorious leader, and her direct holdings. 

1-2 major major in the city, with ~3-5 smaller inside that, depending on how many magical girls they have beneath them. Obviously, the more there are, the less direct holdings you have. 

Normal humans, a lot. Magical girls, up to ~6, though technically you could have more. The only difficulty is that you need to have enough Witches to support the magical girls you have, and if you have too many, you won't be able to unless you go raiding other people's territory. 

Feel free to offer suggestions though if I'm being ridiculous. This is just off the top of my head.