Hubs are part of the USB spec I'm pretty sure. The hub's controller should also handle bandwidth bottlenecks.

As for the hubs in point 2, I am actually using a chain of three USB hubs between my Mac Mini and some of my peripherals (4 hubs if you count an internal one), which so far has worked without issues; I think all three of them caused instability on the USB-A ports. Again, the ports work fine when only one peripheral is connected directly, I plugged in two disk enclosures that saturate 5 Gbit/s and didn't see any issues when reading from both simultaneously.