2g Serpentine Belt Replacement - Replace Pulley also?

When the belt is off you can listen what sound tensioner pulley bearing makes and decide if it needs replacing. If belt wasn’t tightened too much it shouldn’t need replacing. Belt should be pretty lose compared to other cars so it’s commonly over tightened.

Replacing the thermostat requires draining, filling, and bleeding the cooling system which isn’t easy so if thermostat is working wait at least to the time when coolant is replaced.

 

The pulley like most belt pulleys has a bearing in it. Its sealed so not serviceable. You don't list the miles on your car but if its making noise its a good idea to replace it. Mine at 90K miles was fine. I took it out and cleaned it then re-used it.
If the mechanic insists on replacing it buy the oem online yourself. I would not use one from an auto parts store. Same for the belt.

I would not dig into the cooling system. Its very hard to bleed air out of a Prius ICE coolant loop because of the coolant heat storage tank.
Not really necessary either as this engine is very easy on coolant. Easiest way is to just dump the radiator only and fill it back up. No air ingress and its about half the system. Do it again in a month. Btw, remove the plastic engine cover over the rad and fill it up and monitor it using the rad cap not the plastic overflow.
Now, what really needs to be changed is the Inverter coolant. The Inverter is very hard on that coolant. Very easy to bleed that coolant.

 

FWIW, I replaced my tensioner pulley when I did my water pump. You are already there and it is a couple of extra fasteners. My time in this situation is more valuable than having to return at some unknown time in the future to replaces itso I just replaced it while I was there.

As mentioned above the thermostat replacement is a little more involved and not necessary nor in the same service area when replacing the water pump.

 

I had the pump replaced, too.

 

It is a good practice to replace the pulley when the serpentine belt and engine coolant pump is replaced, assuming that your cost of labor is relatively high. I did that.

Replacing the engine thermostat is an activity which is unrelated to the pulley and serpentine belt, so you are not going to save any labor effort if you combine those tasks. However if your car has logged 150K miles or more, that would be a reasonable thing to do.

I posted on how to do all of that work here: How to replace engine coolant pump and thermostat | PriusChat