Arduino & 74hc595 question

Other Hardware General Electronics
3
  1. Yes, yes. I understand that. My question is if Q0-Q7 are using 70mA, does the 74hc595 also needs 70mA or less ?
  2. I understand there is a fuse, set to 500mA if using an USB? Does it mean that it can actually supply 500mA? What changes if I don't use USB but some external power supply?
  3. I'll be using GND pin on arduino, not I/O. Is the same story, about 500mA fuse, with GND pin also?