Read the datasheet. It tells you the frequency for that part and you should have a good idea of your maximum output current.
You can also determine it experimentally. Start with a 4.7uF X7R Ceramic (0805 or 1206 size) rated for at least 6.3V (ceramic caps quickly lose capacitance as the temperature increases and you approach their rated voltage).
Look at the output ripple with a scope, if it's too much, move to a 10uF cap.
Be careful placing too much capacitance on the output as it can destabilize the control loop and actually make ripple worse. (You end up with a few mV of ripple super imposed on a slower sine wave that's a few hundred mV.)
The input cap can be any size, but should be low ESR. Start with 10uF. This needs to be ceramic as well.