If they daisychain like the Avalon4/6 you could buy one controller for like 50 units if you had USB hubs and such.
but with that you have the one single point of failure,
I will probably do 3-6 Avalon's per controller, although its going to be a learning curve for me as I have only set up Spondoolies and Bitmain kit.
Either way I feel this is a more reliable way to go with my mining enterprise rather than attempting to keep Bitmain S9's propped up ahah