I have a metal shop that I built a room inside with lumber and sheet rock. I am going to run 3/4 emt to a large metal juntion box that I have six romex 12/2w/ground wires from the wooden structure inside. Can I run one ground from the main panel to the juntion box and attach it to all the romex ground wires via ground bus that is also attached to the metal box? Should I run a ground wire for every circuit from the Panel to the junction box and if I do do I need to go larger on the EMT? Only five feet away from panel to Junction box.