First general info:
USB2 ports do not automatically provide a 480Mbps connection; the device and the port negotiate a speed of 480Mbps, 12Mbps, or 1.5Mbps.
Depending on your MB, you might have multiple controllers each connected to a single port, or each controller might be connected to two or more ports.
1. You must consult the MB specs. You can also go into the Device Manager and select view by device connection.
2. Probably not. Most mice and keyboards only operate at 1.5Mbps.
3. Probably, but look in the Device Manager.
5. It depends. eSATA is 400Mbps, but the protocol might be more efficient. It also depends on whether your hard drives can saturate the interface.