1) Let keep it easy and skip the punched nuts for now. (7 mm is also the minimal clearance space for the pcb) We will use a similar type of hexagonal m3 stud as you suggested and mount it with a m3 screw through the bottom plate. We then may have the hole sizes in the bottom increased to 3.2 mm. Could you still fit four M4 punched nuts? Please keep the remaining holes (for cover plate and side) as is, we will fit self-tapping screws here.2) The two holes for mounting the top plate may be removed. 3) We would like to keep the folded side flaps, it is based on a previous electronic unit we have designed and build in the past. Does this give an issue for your production machine?4) We thought (anodized) aluminium is better to keep the shipping costs lower instead of using stainless steel. What do you think? 5) We have some difficulties exporting the PCB to a STP file. Is it still required for you, since we skip the use of punched M3 nuts?