I have four USB 3 ports on my late 2013 iMac. (One is obviously for the keyboard.) I have a Plugable 7 port USB 3 hub on one of the ports. All of the hub connections are in use. I’d like to add more ports via another hub. Is it possible to add another hub to the adjacent iMac ports, or am I limited in the total number of USB ports/devices I can use over all of the iMacs ports?
Theoretically USB supports up to 127 devices but in real world situations we’ve not found that to always be true.
Realistically you could probably use 3 or 4 USB 3.0 7-port hubs. Please keep in mind that hubs can only be daisy changed up to a few times, so it’s best to plug the hubs into the built in ports on the iMac.