As far as what to buy, for USB something like:
https://www.amazon.com/Upgraded-Anker-SuperSpeed-Including-Charging/dp/B005NGQWL2/
https://www.amazon.com/Sabrent-10-Port-Individual-Switches-HB-BU10/dp/B0797NZFYP/
It doesn't really matter what USB hub you use, as long as it's at least USB3. If it's USB2 it'll take forever.
I was on a project a few years ago where we were updating about 2,000 iPads using AC2. I used this, plus whatever other USB hubs I could get my hands on. Eventually I was doing about 35 iPads per batch, and I had them connected to that USB hub and other hubs connected to the Mac Mini. Really just any hubs I could find laying around. Some were daisy-chained. I even used the USB ports in the monitor...it was absurd how they were all connected, but it worked fine.
Every now and then you'll have on iPad that spoils the whole batch. It's annoying but whatever. Just redo it. Sometimes it might fail more than once, and if that's the case, just remove it from the batch, update the rest of them, and then update that 1 iPad by itself.