and not just "pullups. The reason for the resistors is that if one pushes one of the buttons, something has got to limit the current, else the LED will go "POOF." While you can, in some cases get away without a series resistor in the circuit if you drive the anode from one port and sink it with another, you can't "get by" with this arrangement, as one can easily hold a button down until the LED smokes.

The LED will have extensive description as to how much current is necessary to set the brightness you desire, as well as the minimum to make it glow and maximum current it can tolerate. If you wish, you can use a series capacitor to limit the duration of the current flow, but that probably won't meet your needs either. If you never have more than one button pushed at once, then you can use a single resistor in the common lead to GND, but I suspect that's not the case.

Read the spec's and use series current limiting resistors to protect your diodes. These will probably help avoid pitting the switch contacts as well.

I assume you intend to drive the optoisolator diode cathodes with the pushbuttons and use the input ports to monitor their status. That probably will, in fact, work, but, again, you need a series current limiter in the anode of the optoisolator's diode in order to protect that diode.

RE