It's a valid concern... I recommend doing the PC version first if you're worried about running both at the same time and bogging the whole process down. Generally speaking, when the ex and I downloaded FFXI at the same time, the PC always finished first but we definitely noticed that it took longer for both than if we had both just done one at a time. Unless your PC is a real junker that barely runs the game, it should finish much faster than a PS4 would or could.