The PROS Editor is the optional Atom editor preconfigured by the PROS team. I do not recommend it; see this thread for more on that.
Unless you already know you need it, you won’t need the toolchain on PATH.
Same for the old programming cable driver — unless you already know you need it, you won’t need it.
If you will be doing Cortex programming, you will probably want the programming cable driver; that will allow you to download wirelessly through the controller.
You will need the V5 drivers for V5 programming.
The V5 Vision Sensor Utility will help you configure and use the Vision Sensor, if you have one and are interested in using it.