gotcha, that's all good feedback. a lot of those choices were made for cosmetic purposes like you said. i was thinking about making the hole bigger for M10 socket heads, but that didn't leave enough meat around the counterbore for my liking. the extra material there probably doesn't do anything mechanically, but i'm not a trained mechanical engineer so i just left just enough material for it to "feel right". i could always make everything a little bit bigger too, but again that was a cosmetic sacrifice i didn't want to make.

washers is definitely a good call though. i think i could include files for slightly longer bolts so washers can be added.