It will depend where you buy it from as to what comes with the G540. I bought mine direct from Gecko and just got the bare controller but I have seen suppliers selling it in a kit with power supply, case etc.
It’s very easy to use and requires no setup or tuning. You just connect a suitable value resistor across two pins of the connector to set motor current i…e no pots to adjust. Actually there is an adjustment but that is for mid band resonance and adjustment is really optional.
It does expect a parallel port connection to the computer but these are easy to source if your computer does not have one. I’m running the G540 under Linuxcnc (free!) but plan to give it a try with Easel ‘soon’. Connecting the necessary control signals from an Arduino is not difficult.
I’ve just finished rebuilding the controller box ( Milling panel for new controller ). All it has in it is the G540, a power supply (48V, 8A) and a few connectors.