Given that all of them are all powered hubs so power won’t be the issue and you have enough space to put them. How much will it impact performance, latency or other things I don’t know about? Or it will straight up kill the port if there are too many hubs?
5 hubs deep and 127 devices per usb controller (not port)
To confuse this more many usb3 or newer controllers won’t handle more than 32 devices.
Now add to that most 7 port usb hubs are actually 2x 4 port hubs.
You may be starting to see why it is so hard to definitively say if a certain usb setup will work or not without testing the actual hardware.
Side note, a lot of usb devices even count as 2 devices due to hw encryption chips, like wd external hard drives.