Personally I would have it done as soon as possible, better to be safe than sorry, no its not too soon, its long overdue and if it were to snap, you might as well say goodbye to your car, yes it makes sense to replace the water pump as the same time too. You can either go lexus or aftermarket, if lexus you can try lexus parts direct,there is a link on the forum. Please get it replaced ASAP, good luck and all the best 👍