Does each thermocouple require it’s own USB port in the computer? Or can multiple thermocouples send data to a single USB data logger?

You only plug the logger into your USB port when you set it up and downloading the data.  You don’t need to leave it plugged in to a USB port while it’s recording.   These devices are meant to record data that is reviewed later, they don’t display real time data on your computer as it’s captured.