Why USB-C has 4 Vbus? And how does it affect my design?
It is to provide a symmetric pinout to allow both connector orientations and it also allows to pass more current over four pins than with only two pins.
The USB standard mandates that all four pins must be connected together at the PCB. You can freely choose to break that rule and use only one pin and it most likely still works but there is no guarantee about that. I don't see any reason why you would want to only connect one pin and I advice connecting all pins.