-The hubs would be sharing the same USB 2.0 upstream bandwidth so the bandwidth on each port would depend on the type of transfers taking place as well as connected devices. However, please note that the hubs would have to be self-powered since maximum output power on the host port would be 500mA and each hub would require the upstream VBUS to be connected to the RESET pin.
-The PWR, OVR pins would depend on the external power switch for each port so you could set an appropriate current limit based on the all the devices of the hub in the first tier and set the hub in Individual powering mode. This would be equivalent to setting the hubs in the second tier in Gang powering mode with a combined current limit in the power switch. Along with this, you could use external power switches for each port in the hubs of the second tier as well with current limit based on each port and set the hub in Individual powering mode.