The opamp can sink or source 10mA (guaranteed) but it can be more.
 When sinking 10mA the output voltage offset is 0.5V, when sourcing 10mA the output voltage offset is -0.5V (output is then Vdda -0.5V
Each of the opamp has dedicated pins, they may be used by another component when not used by an opamp. Since there are different sockets for PSoC4 easiest is to build the project that uses opamps and let the fitter choose the pins. In the pin-view the preferred use of a pin is shown.
3) See the dedicated table chart in this ap note -
http://www.cypress.com/?rID=93401 AN86439 - PSoC® 4 - Using GPIO Pins
What do you need to drive with the OpAmp, there are ways to increase current ?
Almost right. This is an output swing limit, not an offset.
2. When driving high, the opamp will meet spec when sourcing current up to an output voltage of Vdd-0.5V. It may go further at the specified load, but no guarantee. Similarly, when when sinking, the output will drive current down to an output voltage of 0.5V. Again, it may go further at the specified load, but no guarantee.
Yes, output swing limitation. I just had a language limitation. ;-)
Thanks everyone for the reply!
I need to sense three different voltages in the range of 0V-500V DC.
Since the interface has large value resistor dividers (200kohm/1kohm), I want to use the op-amp as a buffer to the ADC.
Also since there are only two op-amps and three input voltages, the op-amps must be multiplexed.
Please could you provide a rough estimation of time, as to how long must the op-amps stay in one position to stabilize its output?