Should do all the belts together at once, and any related parts that need inspection/replacement.
Usually changing the timing belt requires a lot of the engine parts to be taken apart in order to reach it. Since parts are taken apart to do the timing belt, you may as well have them inspected and replace if necessary.
If water pump is being done, you should get the radiator, the fan, the coolant hose, and all cooling related parts checked.
Better be prepared than anything else right?
