Stranded vs Solid Copper

Not getting the point of a home made box, hospital grade receptacles will fit in standard boxes. Not  sure home made would meet code might want to check on that, if there was an accident insurance companies can get a little testy  on such things. 

Yup, expected or intended losses are excluded. 

The plastic box was buried in the wall so far that the electrician used 2 + inch screws to connect the receptacle to the plastic box. When I plugged my Silnote cord  into the receptacle it pushed the receptacle back into the wall and broke the plastic cover.
i could have mounted the metal box right over the existing box, but I thought this might afford me the chance to gain some flexibility and expand the number of outlets to two.

You can get outlet extenders and / or spacers to keep the receptacle from pushing in and breaking the face plate. You could remove the old box and install a double gang if you want 2 receptacles in that location or install another box and run a wire from the existing box to your new box if you want them in seperate locations.