timing belt

So, based on the other answer, replace the timing chain at 100,000 miles? Do I need to replace the serpentine belt at a certain mileage?

No, you need to periodically inspect your belt(s) for wear. Look for cracking, chips, fraying, pieces missing etc. If it has started to squeel especially on start-up or acceleration or is shiney it may have streched and still needs to be replaced. Generally 100k is about the max life from any drive belt. The main drive belt can be replaced in 5 mins in your garage or driveway....super easy.