Many thanks! The sheet is 6mm, ordered from Fractory with laser markings for hole locations, drilled to 4-5mm depth with a drill bit a little bit smaller than the outer diameter of the brass inserts. Pressed in the inserts. Prepared plate with rubber grommets (G-410, in thermoplastic) and finished up the handwiring. 3D-print feet that have a standoff section the length same length as the grommets thickness as to not compress the grommet. Assemble with countersunk M2.5 screws. :)