Lorne, The individual digits will appear to be lit at the same time, but they won't be because of multiplexing. Pins 3 and 4 of the 4553 counter needs a capacitor(1nF). This sets the multiplexing frequency. I never try to run LED's at the maximum current. Your initial resistance of 125 ohms should be okey as the human eye will not see the flicker because of multiplexing.
Keep in mind that the maximum current for the LED's is generally for continious use. If they are being pulsed or in this case multiplexed and they are not bright enough then I would reduce the current limit resistors, but never exceed the maximum current on an average basis.