At what point in time would it be ideal to change my water pump to avoid something more serious?

There is no reason at all to change the water pump before it starts leaking or making noise which may be never. A water pump is not the sort of thing that will leave you stranded by the side of the road. The timing chain is another matter. They typically start making some noise which warns you that its time though so if its running well and not making any odd noises under the hood I would save your money for other things. With that mileage its going to need wheel bearings and axles soon if it hasn't had them already. If he's dieing to spend money have the transmission serviced, replace the coolant, give it a four wheel alignment and maybe some fresh spark plugs and wires. Check it for trouble codes and if there are any address those problems. After that drive it and enjoy it and don't go looking for trouble. It will find you soon enough on its own.