As with most things, it depends. It depends on what these Robots will be executing from an Automation standpoint. What is the process or processes that are being automated? Why the need to run 20 simultaneously? What is the Environment? Meaning, are you planning to run these 20 Robots all on the same machine (Server) or on separate machines (VMs)?
I am sure you could kick off process via something like Windows Task Scheduler, but I would personally recommend utilizing Orchestra tor. Does your design utilizing Queues and Transactions? If yes, then you need to use Orchestra tor for sure.