TCA6416A: Set P00 to P17 to known state before I2C access to set as output.

"If P00 to P17 are all used as outputs and the outputs need to be in a defined state before I2C access to set as outputs is it OK to use pull-up or pull-down on these pins?"

Yes, this is actually what we expect designers to do when they need to ensure the state of the pins after power up but before programing the device is initiated. 

"Any particular value required."

You could technically use any value however weaker (larger values) will generate less leakage currents but are more susceptible to noise (meaning the bias voltage may move when noise is present). Stronger (lower values) will provide a stronger bias but may eat up more leakage current (a bigger careabout in battery applications). Something like 47k would work in most cases. 

Please note that we expect GPIOs not used to also be set as outputs or left as inputs to be pulled high/low with weak resistors. This is to ensure shoot through current doesn't appear. 

Thanks,

-Bobby