I just have to say, I read this thread over lunch today and very much enjoyed it. It reminded me of the dogs on Funniest Home Videos chasing their tales.
I certainly can’t add any professional help, but my pic is my original system from 09’. It has grown to 24 individual audio zones and 10 individual video zones. We have 7.4 in the theater room, 5.1 in the master bedroom, 20+ cameras, lighting, remote blinds, keypads, sprinkler, etc. Lots of drivers and lots of programming. We have a CA-10 because I wanted it, though dealer said it wasn’t necessary. CA-10 is running the director and HC-800 is running zigbee, audio, IR, security interface, etc. So two “controllers” for 24 zones as I believe you are calling them. We have many areas with multiple “zones” within them and it is not a problem.
As for the OSD, we never use this, thus all the additional controllers were not needed.
Also, seems like a good spot to say thanks to all the pros that help out and give advice on these forums.