Proper Chassis Grounding
In the USA these are the issues to deal with for grounding a metal enclosure to UL standards. They are common sense reasons whether you build one for yourself or build a 1,000 per year.

As I mentioned as a comment UL requires that the Earth ground wire be the same gauge as the hot and neutral wire. This is not a problem if it is a 3-wire cable, as all wires are normally the same gauge. If using wire nuts to convert from solid to stranded wire the stranded wire needs to be the same gauge as the solid wire.

As for the chassis ground we used 1/4-20 SS bolts about 3/8" to 1/2" long. A crimp-on lug is the best way to go. Use a hammer if you do not have the proper crimper. You MUST use a grounding type washer, which has teeth both inside and outside, and it goes on the bolt before the lug does to create a very low resistance connection to the chassis. The nut goes on last.

You are not selling it so no need for labels, though at some hardware stores you may find a generic "High Voltage" label you can put on the door or cover. It may remind you to shut off the breaker or disconnect switch before working on it in the future.