I run a 3 camera setup and it works fine for my 10 foot by 10 foot play space. I have a fourth, but I have been too lazy to set it up.

I do run two Inateck PCI-E USB cards so I don't run into capacity issues. There are many reports of issues running > 2 sensors and difficulty getting the Inateck cards working correctly due to driver version issues, USB power management etc.