Serpentine belt is a 5-10 min job, you can do that anytime.
Since you are doing the water pump, time for a coolant flush and 50/50 distilled water and Zerex G-05.
You could also do upper and lower radiator hoses.
You might also do the thermostat while you have it drained, your choice.

Hint: remove the plastic radiator fan module - gives you much more room,
but cut a piece of cardboard to cover the radiator so you don't accidentally stick a wrench into it.