I put the SCRIPTA distro on my RasPi and got it preconfigured as much as I could, but I'm hearing there are issues with chaining large USB hubs together. In other words, if you need more than two hubs you might want to set up another Pi.
The Pi can only handle hubs 2 levels deep. As far as I can tell, the max number of ports at a given level is 7. So, if you have a single level 7 port hub, you can plug 7 into that, and have 49 miners on one Pi USB port. The Pi has 2 USB ports, so, in theory, you can put up to 98 miners on one Pi.
When USB 1.1 was released, and even 2.0, the maximum devices of 127 seemed laughable. (Who would ever need more than 640KB of RAM?!)
I was never able to realize why someone would find it useful to have 127 slow devices connected in this way. Since I can readily envision a large Gridseed farm, it amazes me this max is finally being realized in something useful besides research!