Well if you used the segmented approach you could have a master node on the CANbus network and say 10x Teensy 3.2s controlling 600 LEDs each in 8x strings of 75 LEDs - or however you wanted to break it up. The master would send CANbus messages to tell the actual LED controllers what to do. This wouldn't work fast enough for video or anything like that but for art effects and even for music sync CANbus should be fast enough.
That way you could dedicate one fast CPU like the Teensy4.0 to interface with the outside, calculate the effects and send the commands to the string controller Teensy3.2 units. The 3.2s just listen to the CANbus for messages addressed to them and do their thing with their locally attached LEDs. They can also report back their health and status on the CANbus periodically. All the other string controllers ignore messages to the others and the master just has to listen for those heartbeat messages which can be sent much more slowly say once per second or something. Or each string controller 3.2 might have its own local sensors say in front of each window or something and announce to the entire network the status of the local sensors so the entire system can react appropriately.
This may seem more complex but each node is simpler and all the 3.2 nodes are just duplicates so you could go to 500 windows if you wanted by just adding more 3.2 units and extending the three CANbus wires.
So just start with the whichever master you like to read the music, sensors or whatever initiates the effects and communicate with one Teensy3.2 with an Octo with a few LEDs. You don't need to spring for the full setup until it works. Once that is working, you are basically done. Just add a lot more of the hardware parts and the software is already there. If one node drops off or shorts out or whatever, the rest keep going and the master can notify you of the missing heartbeat from the broken node.
Anyway that's how I would do it. I'm sure you can use a powerful processor like the 4.0 and do it all with one unit but if that unit goes out your entire system is out or if a few LEDs in your 6000 long string go out you could lose the entire display. It always comes down to a bunch of tradeoffs between complexity, cost, robustness and development time. Since hardware is cheap compared to my time I tend to use a lot of simple hardware elements rather than one super complex all-in-one unit.