Ahh gotcha, I do know you have to be pretty particular when installing outlets in the top of something like a table/counter. Depending on codes in your area there are lots of options for popup outlets. first thing that comes to mind is the office desk type: https://www.amazon.com/Pop-up-Power-Data-Station/dp/B00FBU3VHS/ref=sr_1_4 (probably find a cheaper one somewhere else) or https://www.amazon.com/Pulling-Tabletop-110-220V-Meeting-Geckone/dp/B017QZQAOG/ref=sr_1_1 I do know that installing a normal plug just flat on the top of something is a definite no no anywhere. The easiest solution in my mind are metal or plastic (the outdoor conduit kind) under the table with plugs.
For grounding the metal boxes, if you go metal, just tie the ground from the wire going to the wall to a screw along with wire nutting all the grounds together. It's often easier (and proper) to cut a small piece of wire to go from the wirenutted bunch and run that to a screw in the box. Just make sure its the ground and not the neutral/hot wire (generally the ground is the bare copper (romex) or green wire (extension cords))