if you want to use SurfaceMountComponents you may have trouble with the milling machine approach due to constrained spaces...if you only need discrete analogue

if you want to use SurfaceMountComponents you may have trouble with the milling machine approach due to constrained spaces...if you only need discrete analogue or large scale digital boards milling maching is not a problem, a really sweet CNC setup will have a learning mode so you can mill a one off by hand then let the machine copypasta the rest of the boards in large number...look for stepper motor controll projects and raid some dead printers and CDdrives for tasty parts and you are well on the way to a kewlissimo homebrew...