For wiring, when in doubt, go to the source. GRBL Wiki has it all https://github.com/gnea/grbl/wiki/Connecting-Grbl
The wiki has all manner of info - worth spending time getting familiar with it.
I just wired estop to the halt input but a lot of people have a separate estop that cuts all power.
You really should get a screw shield for your arduino, makes all the wires a lot more secure.
You will find all those extra inputs are available on the arduino.