I just got my Raspberry Pi 3 and I am not sure whether or not I can draw 0.6A from ONE USB port (others unused (keyboard and mouse excluded)). Can the RPI handle this? Can I use all slots at once for devices that require 0.6A?
The simple fact is NO ONE can answer this question (due to the lack of published data by Broadcom).
If the hub complies with the USB standard the answer is NO. Many hubs do not, and will supply as much as you want (although often with a non compliant voltage drop).
The Pi can supply TOTAL 600mA from USB, although this can be increased to 1.2A.