How do you determine minimum system requirements?

I don’t have access to a lineup of machines with various configurations to test with. What are the next best ways to figure it out? Just recruit a bunch of testers? Does UE have any built in tools for this?

You can create a virtual machine and limit its hardware. You may not be able to test against specific chipsets doing this, but you can assume the required amount of memory (RAM, VRAM) for devices from doing this.