Because humans do unpredictable things, expect a labor-intensive UAT (humanoid) testing process. Humans follow a prepared script and execute steps over a set period of time to test for errors and performance problems. In addition to testing concurrency, capture other critical information from human testers:
Use of the model with different bandwidths
Use of different operating systems
This data that can help identify and resolve usability issues.
You will not know if the tester follows the script as you might anticipate. If a tester becomes bored or distracted, steps can be missed and areas of the model with bugs can go undetected.