The maximum frequency of operation for the SN74HC20D is 25 MHz.
Yes, the SN74HC20D is compatible with 5V systems, but it's recommended to use a voltage regulator to ensure a stable 5V supply.
The output enable (OE) pin is active-low, meaning it should be connected to GND to enable the outputs. Leaving it unconnected or connecting it to VCC will disable the outputs.
The SN74HC20D can sink or source up to 25 mA per output pin.
Yes, the SN74HC20D is compatible with 3.3V systems, but the output voltage levels may not be compatible with 3.3V logic. Use a level translator or voltage regulator if necessary.